All of my podcasts and talks get transcribed at castingwords.com. They've got mechanical Turk on the backend, so occasionally you get a very bad paragraph or two in the middle, but their turnaround is quick, they're relatively inexpensive, and it beats the heck out of "no transcript."
You should try looking into MobileWorks. Recently they've focused more on human generated lead gen, but they might still/used to do transcription as well. Their crowd is generally much more reliable than MTurk.
I'd like to make this happen.