Ford Taurus

I have an automatic transmission, 1999 Ford Taurus with 77,000 miles on it. The gas pedal is vibrating when I accelerate (not when idling), and there's a buzzing noise coming from somewhere up front. The guy in the repair shop says he thinks it's the transmission and wants to open it up to check. Just checking costs nearly $200. This car has been babied (regular fluid checks, careful driving, etc.) So it's hard to believe the transmission went already. Any ideas on what else this could be?
What's the cheapest way to get the transmission rebuilt if it comes to that?

August 18, 2007.

Have the codes been checked yet?