Extending by mileage is going to hurt your wallet. But after 5 years if you haven't reached 100k km you can still extend by time only (another 2 years). It's cheaper and probably worth your while. Despite those cars being very reliable and trouble free. (with odd exceptions of course).
For petrol motors from an economy point of view get the manual. Obviously from a driver perspective as well
For that kind of money I would rather suggest a 320d. Coming from a converted petrolhead, I'm quite enjoying my diesel now. They are frugal, fast (Especially in manual) and fun. The autos are normally better suited to the diesels IMO.
Hope you find the car you're looking for.