172k miles is a bit high. Keep in mind that the 750's can be very expensive to maintain. $3000 isnt a bad price if the outside is in decent condition. Keep in mind the windshield isnt gonna be cheap. If the moulding that goes around the windshield can be re-used that will save you quite a bit of $. If the moulding and the windshield must both be replaced then its most likely gonna be over $600 (aftermarket) $1000 (dealer)
If you can do some of the mechanical work yourself then that will help a lot but the v12's are definitely more difficult to work on. You mentioned it needs fuel pumps, I assume you already have a price on those? if you are buying the vehicle in a non-running condition and the seller isnt supplying a smog certificate then I would be very very leary. The intake blocks on that engine commonly leak which is an expensive repair along with other things such as failed pcv valves etc so if its not running then once you do get it running you may find that you have to sink additional $$$ into the car to get it smogged (if your state has smog laws of course)
Anyway, not trying to scare you away but just letting you know some of the things to consider and watch for.
Best of luck.
P.S here is a link to a couple sites which may help you..... e32 site with repair writups Online parts catalog with part #s and prices