What's a fuel pump cost for '90 200qt?

I took a '90 200qt for a test drive today and it is making a constant buzzing sound from the rear of the car anytime it is running. I read on here someplace that this indicates the fuel pump is on it's way out. Now I can't fiind the post anymore. Everything else (except for some minor things I can fix myself) on this car checks out ok and I really like this car. The local Audi dealer quoted me a price of $464 for the pump and about 1-1/2 hours labor. Can one of you experts please tell this greenhorn if these pumps are available elsewhere and at what cost? Also, is this a job a relatively competent shadetree mechanic can perform?, or am I stuck with taking it in? At this point the car runs great and the pump doesn't seem to be causing any performance problems.

I think the owner will work with me on this, and I would rather have him give me a better deal on the car than have him give the Audi dealer a bunch of money. I think I can use this to bargain a little with him. Also, in the location where he lives, about the only place to get an Audi fixed is the local Audi dealer. I live a couple of hundred miles away and there are lots of foreign car repair shops around where I may get a better price.