I've tried Dragon Naturally Speaking, and the problem is that you have to train it to recognize your voice. So if you were going to dictate a book or your own notes, it works. But if you're trying to transcribe interviews for other speakers, it doesn't work so well because it only knows YOUR voice. It was a few years ago that I used it though -- maybe it's better now.
There ARE cheap transcription services out there, but it only makes sense when depends on whether your pay rate great exceeds the rate of the transcriber.