Looking for a free plugin for selling photo prints

After a month of messing with stuff, stumbling, backing up and trying again, I’ve got a basic website that lets me display images for sale. I THOUGHT I could use the “to purchase contact me” method, but it’s looking like I’m going to have to use some kind of shopping thing…

SO, I’m trying to find a plugin store or shopping cart or whatever I need to let me create a pricelist so prints of different sizes can be ordered. And a buy button – it would be nice if it could be available for images in the Lightbox, but worst case at least a user should be able to select from the thumbnails. Whatever it is can use Paypal, but unfortunately, I need one that’s free ’cause otherwise I may as well stay with what I’m currently using and let them have all the headaches.
SO, can someone point me at a free plugin that’ll enable me to display and sell multiple sizes of photo prints and downloads?