Does it start? If so his value for the car seems perfectly reasonable but his valuation of what it would cost to put right is erm.. optimistic! It depends a lot on how much you can do yourself but things I had trouble with on a 944 I bought with no mot were..
Handbrake - cables and drum internals rusted and seised, not cheap parts say £300min plus £300min labour if you cant do it yourself because it goes behind EVERYTING and I seem to remember it was about 4-6hours labour with getting all the rusty bolts loose. The mechanism in the drums WILL be seised or well on the way.
Rusted cills etc - will need inspection but mine had to be cut out and fresh metal added in to pass the MOT because of their proximity to the seat belt fixing point allow £200min. ALSO check hard around the number plate and in the rear boot wells behind the rear wheels. Mine was ok but these are areas for rust and not easy or cheap to fix! Also if its been messed with to fit later bodywork there may be other areas of rust to look for. Be careful.
Brakes - I'm pretty sure that the 2.7 lux still uses sliding calipers like the 2.5 lux if so lucky you! These are far less problematic and much cheaper to fix. Allow £400-500 for disks, pads and fluid plus labour if you cant do it of another say £300.
Wipers - expect to have to do something. Mine luckily only needed a new relay (£10), new hoses for the washer jets and the normal fix to the ball joint (which is free and easy to do)
Headlights - do they work on dip and main beam properly? Check hard because the wiring is crap and breaks mine needed patching in with new wire where it bends. Also the earth point rusts to buggery and on mine needed cleaning up with acid and wire wool. Again cheap so long as the mechanism works ok.
ARB's and bushes generally - expect to replace a few bits here. Varies car to car but there'll be something failed if its been sitting around. Allow £200-400
Tires - may seem minor but its still a big cost! I paid about £600 for the 4 new ones required on the one I bought (but that was a turbo)
Rubber seals - like the boot, doors and roof one will be worn/perished but don't go to Porsche. Buy standard door seal by the meter from somewhere like halfords and it'll cost you very little allow £40
Service - you'll almost definately need a set of HT leads as well as plugs maybe a rotor arm and obviously an oil change (I recommend mobil 1 15/50. Also given its situation you'd really need to do the belts. Get the parts yourself and find a good local its a simple car and doesn't need anyone special to do this kind of work. Allow £500 for this lot of £300 if you do the work yourself.
Steering - the power steering hoses will be leaking.. don't worry about that just put a pot under the fluid tank remove the hose and take the rusted jubilee clip off. Cut the first 10mm or so off the hose, clean the whole lot up and re fit tightly with a fresh clip. So long as the pumps not leaking it'll be fine. Allow £10 inc fluid.
Basically with a couple of unforseens (like maybe a cracked radiator which is a weak point, clutch cylinder, leaking hose, failed temperature sensor, failed relay) which I've had on the two cheaper 944's I've bought your probably looking at more like £2000 over the first 3 months of ownership. I hate saying it because I would really really hate to put you off buying a car you'll NEVER regret owning but you've got to know the truth of it's cost because it just WILL be that one way or another.
All I can say to finish is if the engine is ok and the basic mechanicals aren't too worn, once you've got it up to scratch it won't let you down. These cars are REALLY built to last and are fantastic to own and drive. I can't tell you enough how much you need one of these in your life. It's no more expensive to keep a good Porsche running than a mk2 Golf. You've just got to get it up to scratch.
