Hi. Everyone's right - get a turbo. A good one with service history is within your budget. Of course some things are expensive to repair but if well maintained should not be a problem. I've always got 20+mpg and the tyres don't seem to wear anymore than a 'normal' car, although they may be more expensive to buy initially if you go for quality.
The only part of Impreza ownership I find expensive is insurance. After shopping around, I ended up with £1400 from Tesco (Have to have a Tracker fitted). However lots of the guys on here will have got it cheaper, some may be more expensive. Depends where you go and in some cases who you talk to - 3 Tesco Ins employees gave me 3 different quotes. One of the problems is, in my opinion, lots of insurers are confused by the model range and in particular, Japanese imports.
Anyway, good luck with your search for a car. I guarantee worries about the turbo breaking, etc. will vanish the first time you bury your right foot in an Impreza turbo.