It will completely depend on who you sell it/them to, and what it is you're selling.

There are a number of established portrait photographers around here that will charge you $100 for a 5x7 inch print, some smaller operations (out of their home businesses) that might charge $25, and some people who will sell them for $10 (mostly event shoots from weddings to car racing shots to fans).

Go around your area and find shows/displays/community events where they're selling photographs (I'm going to guess you're maybe selling landscapes and the like?) and get a feel for the going prices in the area.

You can always try to sell to stock agencies like picturestock.com and photos.com?

Good luck - hope that helps-
-Lew ;-)