If you don't have a Store subscription, you get 50 free basic insertions per month, and after that they're 35 cents each.
If you have a Store subscription, then the level of the subscription will determine how many free insertions you get and what they cost after you use up the free ones.
If you don't pay your eBay bill, then eventually it will be sent to collections and will affect your credit rating.
Fees for sellers who don't have a Store: http://pages.ebay.com/help/sell/fees.html
Fees for Store subscribers: http://pages.ebay.com/help/sell/storefees.html
