Welcome to Gaia! ::

(hopefully you see this reply, I know this post was made a few months ago)
Big wall of text ahead

It depends on the convention you're going to.
It can range anywhere from $20 to $100+ depending on which con and the table size.
From personal experience, you still have to buy your con admission on top of your table fees, unless the con has some sort of deal.

Do check the artists rules on table coverings and displays for your con first but here are some tips I can give you from personal experience.

Bring a table cloth/ some sort of table covering.
Some conventions do provide table coverings, but it never hurts to have something fun and colourful on your table to spice it up a bit and help you stand out from the crowd.
-If you want to go pricey, get a couple yards of solid coloured or a cute print of fabric that won't clash too horribly/detract from your work and cover the table with it.
-If you want to go cheap, do like I did and check out a local party store. You can get some nice solid coloured plastic table cloths for $2-5 (I went with a light teal, myself).

Are you selling craft items(plushies, charms, hats etc) or paper based things (prints, stickers, bookmarks etc)?
Either way, you definitely want to have some displays for your work, because trying to lay everything flat on a table can get tricky.
A nice backboard to pin sample prints to is a good idea.
Or having a binder people can flip through.
-For plush items, look around for little baskets or boxes to hold and display them
- For jewelry, hats or some cosplay items, make sure you have some sort of stands to display them so people can get a better idea of how they would look worn instead of just laying flat on the table.
Wig heads are good for hats and you can find jewelry displays/holders plent of places.
(I raided a Claires and a craft store for some nice, inexpensive jewelry stands and displays for my table.)

What does the best in artist alley?
Series wise, try to find things that are popular and current, but don't be afraid to mix it up with some old stand-bys.
While prints are great, useful things - buttons, bookmarks, hats, jewelry, plushies, etc tend to do well.
They are something someone can use, not just look at and be pretty and people like that.

Signs, prices and contact info:
-Try to have a sign saying who you are and/or the name of your table.
If doesn't have to be fancy, but should still look professional.
No sharpie on a page ripped out of a sketch book.
- Make sure you clearly mark all of your prices for all of your items and/or a price list.
- Have some sort of contact info available, especially if you do commissions outside of the convention.
Business cards are a REALLY good idea to have.
There are websites that will do them for "free"(+shipping) or low cost, but you can get some basic ones done at a local print shop/Staples/Kinkos/UPS Store, too!


General tips for having a table:
-Be nice to your customers!
-Be nice to the people you are sitting beside. Seriously.. you're stuck with them all weekend.
-Have a way to store all your stock properly so it doesn't get damaged going to the con, at the con, or on your way home from the con.
Folders, binders and rubbermaid totes are good ideas.
-If you're allowed, bring some snacks and drinks to have with you at the table. You don't want to be getting dehydrated or super hungry.
-Bring enough stock!
(I made this mistake last year - I made some plushies and I sold out within 30 minutes of the artist room being open because I only brought a few.)
-Have a LOCKING cash box. You don't want anyone stealing your hard-earned money!
-Bring a "float" so you can give people change.
Some fives, singles (or toonies and loonies if you're Canadian, like myself) are good. You don't want to really go any smaller unless you're not dealing with whole dollar prices. To make it easier on yourself, keep things at whole dollars.
-Have a buddy help you if you're allowed. That way you don't miss out on the other fun activities at the con.
-Don't sell yourself short, but don't charge TOO much when it comes to pricing.
-Check out the other artists before hand if you can so you get a good idea of what is being sold. Some cons will have a forum. Check out other artists wares and prices there. That way you get a feel for how much you should charge for your work and you get an idea of the types of things being sold.
Which brings me to my next point...
- Have a unique product! There will probably be a lot of people selling prints. Try doing some bookmarks or post card sized prints or even some crafty type items. Watch that you aren't selling the same thing 10 other people are selling!
( For example: The past couple of years I've had tiny top hats at my table. Last year, four or five other artists decided to have them too. I didn't do as well selling them because of that.)
-Don't be disappointed if you don't make a bajillion dollars.
Sometimes when you're new to artist alley you might not do as well as established artists. Don't get upset and claim that you will "never do another con never ever ever again". Try again the next year, or at a different con, but don't give up after your first if you enjoyed it!
-Have FUN!

I think that's it, but if you have any more questions, please let me know!
I know it's a lot of info, but I hope this helps!
C:

You're welcome! I'm happy to help!
With clothing, I'd stick to smaller items. Again, it's a lack-of-space issue.
If you do bigger items, take commissions for them before hand and have people pick them up at the con.

That's a good plan. When ever you're ready. c:
Just make sure you have business cards!
(Do you have a paypal account? It's a good thing to look into if you're doing any business online.)

CCs? Credit cards?
Hmm. I'm pretty sure it is really expensive and really impractical for an independent artist to rent or buy mobile point of sale(debit) machines.

I know my convention isn't a mega huge one, but only the biggest vendors have those machines.
Most of them take cash only and ALL of the artists take cash only.
It's likely the same at your convention, unless you have a professional artist(s) with a booth.

A few artists at my convention (myself included) run or are working on setting up small businesses. They all deal in cash and paypal transactions only. ( I was just asking about the paypal. Some people don't have them and they're a good thing to have.)

My mother ran a small business for a while. It takes a while for it to get off the ground, so advertisement is good. BUT starting a business is a lot of work, keep that in mind.
I know she looked into getting on of those machines but didn't end up getting one because it was impractical.
A quick google search tells me the machines start at $1500 or are anywhere between $50-$100/month (+ data plans) to rent or lease.
Unless you're planning on doing A LOT of conventions/shows (one or more a month) it's simply not worth it.
You said your business was going to be online, right?
It's just easier to deal with paypal.

Ok. Well, like I've said it differs from convention to convention.
Tables at my con sell out FAST. Like with in MINUTES of going on sale.
You'd probably be best getting one as soon as they are on sale for that year.
Keep an eye on the website for your con.

As for the displays: Hey, what ever you feel you need, works.
I can only tell you what I know from personal experience.
It just sounds like you want to have A LOT at your table, so if you want to have everything, it's better to keep items small.
Or specialize in one thing. Quality over quantity, y'know?

From experience, most artists that I know take cash only.
It's just way easier.

Also, I don't want to be rude but, that's really not a great attitude to have.
If you want to be taken seriously and respected by other artists, you need to show them some respect.
Think of how hard you work on your art - they probably work just as hard.
I can sew, paint, draw, and sculpt, but I never consider buying art from another artist to be a waste.

What Raya Kioma said are really good points.

Having someone to help you at the table is the biggest tip in my book. Not only can they work the table if you need a break, but they can also help make sure stuff isn't stolen.

My first time working at an artist ally table I had a piece of work stolen, so you may want to find a way to make sure that people can't do that. It is one of the trickier parts of working AA tables.

Bring extra material with you as well. When busyness is slow it's nice to make things to put out.