Audi purchasing help

[Tim Tompkins]

I have the opportunity to buy a '89 200q for ~$3900
It has ~100,000 miles and full service records.
Interior is in better that good condition and ext is pearl white.
Now for the bad parts:
passenger window does not go up/down
trunk doesnt open with key.
windshield is cracked
ac is low on freon.
the factory boost guage doesn't seem to work.

Now for the questions:
Is that a good deal? kbb and the like say ~$7000
What do i look for mechanicly to be wrong? (tierod ends?, rear dif, turbo?)
Where should i look for rust?
Electronicly is there anything to look for?
Am I looking in the right spot for the boost guage? (next to the trip computer)
Is there an easy way to tell if you are getting boost or an easy boost guage 
tap point?
Anything else that might help?

Thanks for any help,

Tim
'92 Mitsubishi Galant VR-4 #893 (AWD, Turbo)
soon '89 Audi 200q (maybe)