I bought a car in similar circumstances earlier this year. Mine is an 91H S2 with 140k on the clock (
Clicky Here) It had been standing although it had been mot'd and taxed each year and had any issues dealt with so it had new brake pipes on the rear, handbrake cables and tyres . It was sold to me by the previous web editor for Fast Car magazine ("Wild Slag") where it was featured as a staff car in 2001/2002. As they blagged lots of stuff for their cars the service history is scant - apart from a couple of big bills from Parrs motorsport and from CMS Porsche (Telford) who supplied it to my seller. It was advertised at £1.5k with a noisy gearbox. When I drove it, it had very noisy transmission and jumped out of gear and I embarrasingly negotiated an extra £50 off.
So far I have spent around another 1.5k. I have replaced the gearbox, rear fuel lines, cv joints, rear shocks, sunroof seals, hatch seals, rear light clusters, hatch pins (although I need a new hatch now!) service items (plugs, fluids & filters etc) return springs for the handbrakes, brake dust shields, accelerator cable, pedal rubbers and some other bits and pieces. It's nearly, very nearly on the road again - and I suppose it is then I'll find out what else I need to do.
Recently prices of reasonably maintained S2s seem to have taken a bit of a fall and wonder if I've done the right thing, i..e perhaps just spend the £££ on a decent runner. But then you'll always need to spend money to fix / maintain any 944 that you take on and at least you have the satisfaction of knowing things have been done properly.
I would say 1.5k sounds about right provding the sills are OK and the mechanicals check out.
Phil
(sorry for the ramble)