Well, for what it's worth, I'm legally blind (I have enough sight to read a computer screen up close, but not enough to drive). And I have totally blind friends who like the idea of a paid service like this. (I personally know the guy whose blog post I referenced in the addendum to my first post.)

Thanks for your input. As I wrote, I'm mainly worried about the tendency for pro-bono systems to get corrupted when you introduce money into them.

BTW. How big payments you had in mind?

If blind are willing to pay and volunteers are willing to help for free, then all the money can be spent on innovation. Sound like a perfect business to me, as long as the volunteer return rate is good.