Welcome to the forum Jon.
Others on here have much more knowledge than me, and no doubt will be along shortly with some useful info, however for what it's worth here's my bit.......
I've had my S2 coming up to six years now and have not had one day when I have thought of getting rid. It's a great car, really useful as an everyday driver, does everything I want it to except attract young blondes..... but maybe it's not the car
My S2 (3.0 litre) averages 28mpg because I drive like a vicar, but if I'm just driving locally I get a lot less. According to the manual it says Urban 19.8mpg, 38.2mpg at a constant 56mph, 31mpg at a constant 75mph... but I wouldn't know because I've never been that fast as the limit's 70mph

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The 25mpg is an average, therefore depending on the type of commute you may find yourself using up to 2.5 to 3 gallons of petrol a day, 12.5 to 15 gallons a week, 56 to 67 litres a week x £1.36 = £76 to £91 a week on fuel just for the commute.... and it won't be going down anytime soon.
A budget of 'a grand or two' may buy you something usable. I wouldn't bother about mileage (mine's on 209000) so much as condition and service history - the main thing being have the belts been replaced etc etc. My first 944, a '89 2.7 Lux, and my current '91 S2, have been one owner full service history cars and I have not had any major problems with either car. Be aware that if the clutch goes it's £700 to have it fixed, if the cam belt goes it's thousands.
It's not the lightest car to drive, in fact if I'm going locally I usually use my wife's MX5 purely because it's so much easier to drive and more economical.
If the fuel costs put you off but you still want to get into a Porsche, I would consider a late 924, a 2.0 litre one (the 924S has the 944 2.5 litre engine so it's back to fuel consumption). They are more or less physically the same but for the wide arches, but general running costs (parts, fuel, tyres etc) will be lower. You will find a good one for your budget.
Also, if it's easier for you both cars are available as automatics - but fuel consumption will suffer.
Hope it's been useful.