DO NOT BUY IT for that price. They can, should and will come down.
My parents just bought a 1993 Park Avenue Ultra in damn near perfect condition (only needed the coolant temp sensor) with 63,000 miles for $4000. Absolutely no damage at all. I too has everything but the sunroof. It has the Gran Touring suspension with the 16" rims, and anything else that could be had.
At the same time they bought that I thought they could get one for cheaper and sure enough it took me only 10 seconds on www.msn.com
and I found a 1993 Buick Park Avenue Ultra with 113,000 miles on it from the original owner for only $1800 needing tires only. Too bad I din't try and go look at it before the weekend (3 days later) as it sold the day after I called.
4 years ago my parents bought a 1992 Park Avenue Ultra for $2500 with 130,000 miles on it. Given that'* kinda high, for the dollar you couldn't beat that.
I don't know what websites are for buying and selling used cars in your area, but you might try:
(newspaper classifieds from major regional papers)
and I am sure there are a load of them.
Anyhow, good luck and be sure to check in here before you dig yourself a hole -we're watching out for you and everyone else here.