How much is it to be a vendor, not permanent

It varies with how much space u rent. Need to call and ask about the different sized spaces.

http://www.fleamall.com/_pages/sell.html Here are all prices you might need.

Used to be like $10 to set up a "little garage sale".

Thats a question you should call in to them directly and ask. That way you are not misled and you'll know for sure. 😉