Mate, WRX's are poser cars these days.
If you're keen on one I strongly suggest you find a GC8, or if you can find a version 3 - 6 GC8 STi.
These are real sports cars.
Anything after about 2000-2001 is a "Look at me" wankers car. They're not fast, they don't handle all that much better than a Commodore and aren't built any better. Aftermarket parts are expensive, and result in little gains. Second hand OEM parts are also expensive.
At the end of the day, you aren't going to get a powerful car (200kw@w is pushing it) the acceleration is all in the gearing (4.11 final drive and close ratio gearboxes). The gearboxes themselves are shite. You WILL break one if you abuse it. I'd rank them just about the Aussie 4speed for durability.
If you plan on touring some twisty roads with some gusto, then by all means.
If you're like myself and live in a country area with nothing but straight roads and a long way to anywhere then forget it.
In my honest opinion, you're better of buying an LS1 equipped Commodore and putting in a short ratio diff. If only to save a packet on your insurance. (Which isn't likely to ever get under $1500 regardless of age or history)
If money is no issue, and you want a Japanese performance 4cylinder then look at an older EVO or anything fitted with an SR20t.