I think Vince (who owns one) might disagree that a 996 is cheap to run!
Yea mine certainly hasn't been, I have owned it (1999 C4 Cab) since Feb 2012 and in that time I would say it has been on the road for approximately 8 months. I spent 16k on the car and have put approximately 7K into it since. I will give a quick outline of my issues and possible other issues.
First up I started to get an intermix, oil in the cooling system. First time the engine was out I replaced the oil cooler, a metal coolant pipe which took 3 months to get here which had to be ordered from Germany and had all the manifold bolts drilled out as they were totally rotten. Total cost ended up being just shy of 2.5k for the work. They were sure the problem was with my oil cooler as it failed pressure tests.
A few weeks later, massive amounts of oil in the water again. So out with the engine again, this time both heads came off and were sent to a specialist. The left hand side head had developed a crack which basically ran the length of the head, a search got underway for a cylinder head, Porsche will sell you one which if I remember rightly was somewhere in the region of 3k. That wasn't really an option, in the end It cost me £1500 and a good few months of waiting. I ended up giving up the search for a new head and took my head to a local head specialist called benchsound who reworked my original head for me.
New gaskets, head bolts, rear main seal, clutch & release bearing as well as a load of other parts I needed to put it back together plus labour at mates rates and before I knew it I was another 3k in.
Took it to get its MOT when I finally got it back and as it was on the ramp a seal gave away on the oil cooler. So it went back in my garage again. I replaced the seals myself on the cooler, realistically at this point I can put it back on the road but I decided to give it one last flurry before I do and a couple of weeks ago bought some service items for the car before I put it back on the road, having taken apart the front end, both the cooling system and air con system were both shot. so a trip to design 911 and I came home with:
Uprated metal blade Water pump - £160
Uprated Low temp thermostat - £190
Radiators - £130 each
Air con kit to replace the rads and dessicator - £200
In total I spent £1100 on parts that the car needed to do with the cooling system and am fitting them myself.
So granted first time around things were missed, and money was wasted in labour but realistically spending almost half the cost of the car again to get it right can be what your in for buying at the bottom of the market.
My 10k Boxster S on the other hand was perfect. To find out you pay your money and take your choice.
Other well known issues with this engine (the 3.6 as well) are bore scoring, cracked bores, Intermediate shaft bearings going causing havoc with the bottom end etc etc To be honest there are all kinds of issues that you read about, some people think that up to 10 or 15% of cars have these issues others suggest its as few as 3-5% of cars that have issues. It's down to whether you like those odds or not. For me my cheap 911 wasn't so cheap but is a good little project car.
I wouldn't imagine mpg figures etc would really matter to be honest and i cant imagine they would be much different from the 2.5l z4, but for what its worth anything from 18 - 32mpg was possible depending on if you decide to give it a hoon or not.
Edit: Thinking about it op should buy a Boxster S, they are fantastic cars.
