Hi Lightning
yes at $10 a pop, you'd definitely get me to part with my money, but I'd have to say, not that often. What would tempt me (and what is missing from the market at any price) would be large, mature trees, the oaks, beeches, chestnuts, (and the now sadly missing) elms of my childhood here in England. Most of the stuff I see from Xfrog or Onyx looks just too small.
I don't know how big a market you'd get though. Can I make a suggestion? Why not contact Dan Farr at DAZ3D with a view to possibly collaborating with him? He seems to have a vision for making good quality models available cheaply, and he already has a huge customer base. I know it means taking a hit on the percentage of the takings, but if you sell 3 times as much at only half the take - you still win. An excellent plant modeller called Lisa Buckalew seems to have sold some serious quantities of her stuff through them. Might be worth investigating....
good luck whatever you decide to do