From the ArcaMax Publishing, Jokes Newsletter:
http://www.arcamax.com/news/jokes/s-371103-106047
Dentist: I have to pull the aching tooth, but don't worry it will take
just five minutes.
Patient: And how much will it cost?
Dentist: It's $90.00.
Patient: $90.00 for just a few minutes work?
Dentist: I can extract it very slowly if you like.