Usability testing for open-source projects?

I'm working (slowly) on an open-source project, and I was hoping to do some usability testing once it's a bit further along. Also, hopefully the GIMP devs will notice this question ;-). I'm not sure how much can be done for $0.00. I can con friends/family/coworkers into helping, and I can use a free screen recorder, but the project is targeted at a fairly limited audience (technical artists working on shaders), of which I know 0. I'm hopeful that maybe some users on the wide interwebs would be interested in helping, too. The problem there is how to connect with them. I've read articles on remote usability studies, however it tends to depend on pay-by-the-minute services and expensive screen sharing software. Anyone with experience doing testing on the very cheap have any suggestions?