I wouldn't say our average tester has given us $25 worth of testing. But some definitely have, even more than $25 worth. Separating these after the fact is potentially sticky.
For my startup, we're providing a service we'll be charging for monthly. All the beta testers will get some kind of discount we've yet to figure out yet (a few months free, most likely, or some steep discount) and all beta testers actually telling us about issues something probably double that if not more.
I guess I just don't like the idea of rewarding someone giving me absolutely nothing in return equally as someone giving me invaluable amounts of help.
Btw, What's your startup, silencio? My email is dani.fong at gmail.