Welcome man
You will be hard pressed to find a GC8 with good Km's and history. It took me a year of looking to find a decent one that had good km's and wasn't asking $16k+.
There is currently a MY99 on carsales with 90,000km for $14k but I think you could grind him down to $11-12k seeings the owner needs to move over seas.
The problem with the dakdak is too many noobs just wack a boost controller on and wind the wick up to 16-18psi because they read it on the forum that its safe to run like that, so be very weary of wrx's that run boost controllers without any form of decent
ECU. Hence the reason for most wrx's you see for sale which have had a recent engine swap or rebuild...
The things that tend to be on their way out on a GC8 are generally :
- Radiator (they are known to crack on the tank ends)
- Fuel pump
- CV boots (which when left split cause fucked CV's)
- Alternator
- Gearbox syncros
- Rust around window sils or boot
- Power steering pump
- Coolant tank.
- AFM (you will be changing these alot you you don't maintain them)
To get a low 12 in a GC8 you will be looking at fitting:
- Bigger injectors (or Decap standard if your into that kinda stuff)
- New intercooler (Bigger TMIC)
- Bigger fuel pump (Walbro for around $120)
- Larger turbo (Plenty of options for bolt on)
- Aftermarket
ECU (PowerFC, Vipec, Motec etc)
Also invest in a decent box if you plan on working it hard. The Sti 6speed conversion is generally the one to go for.
I ran a MY94 of which I upgraded the above and ran mid 12's on a stock motor, turbo (albeit a TD05) and box. Never had a issue at all.
From there, your looking at EJ207 block which can be had for good coin etc etc
In short - plan for around $8k+ on top of purchase price of wrx to run a reliable mid 12's.