ETA: what kinds of hourly rates do tutors tend to make? I'm just curious how that market plays out.
What I'm afraid of in this space is that you're going to have a mix of (a) unaffordable good ones and (b) cheap, less capable people.
It depends on location and opportunities but half-decent freelancers tend to be over $100/hour where I am (New York). People will work at a lower rate for good-citizen reasons (and because they care about the technologies, want to meet new people) but that component is limited and will never get to on-demand service.
Pointing out freelancer rates in major cities is also not representative: Lower cost of living cities have lower market rates for freelancers. When you're delivering the service over the web as we do with http://www.thinkful.com/ each party (the freelancer and the hirer) can split the cost savings.