James Sexton mentioned $2,000 in one of his interviews (which are excellent, BTW). Was he expensive because of time spent in court, defending the prenup?
The most common failure is not having a prenup at all, followed by getting cheap and making one without any lawyers. In court, the other person claims they didn't have legal counsel, and the prenup gets invalidated. Both people need their own lawyer when they review a prenup. There's a few other gotchas easily solved by a professionally written prenup.
I liked Rollo Tomassi's (The Rational Male) interview of James Sexton: