My advice is to buy one off a member on here first. After that. You need to be looking at latest model lowest mileage first. "suck eggs eh" As stated before depends what your after. If I were you, which I'm not.... I'd go for a decent Type R or RA for that sort of money. You'd expect to get a decent one for that budget.
Have a gander at www.type-ra.co.uk to get an idea
Like I say, depends what your poison is. Power / drivability (real word?), comfort, both or one of the above.
I've owned a 01 WRX tuned from new to 285PS and now I have a 01 WRX STI Spec C Type RA. If I had the choice from the beginning the RA would win. I can live without A/C elec windows, elec mirrors, C/L etc etc. If it was a commuter I'd probably want that lot.
Failing that I also have an STI v2 track slag and a 93 WRX wagon. Well below your budget (not that I'm selling) but you could look at something like these and spend 3k on tuning. Just a thought.
Wish you luck buddy, and if you need someone to look over a motor and I'm available. I'll be there.
Aston