It is a cost that depends on the show, but overall, assume that the table, your supplies, and the displays are going to be much more than $500.
I really enjoy being a vendor, but it is also fun being a customer walking around. Being a vendor means you need to stay behind your table for the most part. Being a customer means you can be wherever you want.
Being a vendor means you are always talking to customers, showing people your stuff, and being a great host. They are visitors at your table. Make them know that they are appreciated!!
Its fun, and a lot of things happen before and after the show. That is always fun as well!
Its a great time!!