£8k should see you into 2008 facelift territory which is where my money would go. Think they look better and nice little improvements on the interior.
Try and get a non-modified version too.
Common issues:
- Worn bushes (check for serious steering wheel wobble)
- Oil Diaphragm (fixed on facelift models, but listen out for a whining noise from the engine bay)
- Clutch (if it's been tuned, check for slip, stick it in 5th at 30 and put your foot down, it shouldn't slip)
- CV boot (drivers side housing is known for splitting, only £40 to fix, but if it hasn't been fixed, then a dry CV joint will cost £££)
Turbo housing was also improved on the facelift, so this should be fine too, but have a look for cracks.
Other than that they are very reliable, and mine hasn't cost me much to maintain over the 3.5 years I've owned it. In fact only petrol/insurance/tax have been more expensive than the 1.6 Mk1 Focus I owned previously.
I'm selling mine shortly if you can wait
