As far as I know, with a standard account, you can only sell prints at a standard super-low price (for which you get no profit), but in order to set your own print prices (and make profits), you will need a pro account. (Although I have sold prints at my own set prices through privately emailed requests, and I have a mid-level account there.)
I haven't checked in there lately. Have they started the stock photo thing yet, or something?