info on 200 sx

Driftard abuse, chav damage.

I'm assuming it's the S13 generation, they get very rusty under the rear spoiler (to the point that big holes form), head gaskets blow if not looked after well.

Simply put £300 = spares car when you're talking about an s13. Body rusts, engines wear and blow when not properly maintained. Brilliant cars if you can find a decent one though ;D

As said above big ends failing due to poor servicing or too much boost. Steel sumps can turn rust and turn porous. Rear subframe bushes. If its an early car the brakes are too small in diameter and are pretty piss poor.
Rust will be the main problem if you are wanting to keep it on the road especially around the front chassis rails. Check those out if its going to be used as a road car.

£300 is probably about right for a tired example.

Good car and I would still have another one though.

check the tailgate,chassis rails, sills and the cross member in front of the rad for rust. check for signs the rear lights/bootseal is leaking. check the play in the turbo (bring a flat head screw driver, takes seconds to pop the intake pipe off to check.) rev the car slowly to 3.5 k and let it drop off if you hear a knocking on let off, big ends. rev it and check for smoke from the exhaust, also let it idle for a bit to make sure it doesnt smoke after a while(turbo). check for noise from the gearbox. missfires are also common.
personally i would rather get a clean shell with a bad engine though as they do rust pretty bad but engines are easy/cheap to get. people sometimes let good ones go for naff all cos the garage tells em how much big ends or whatever will cost. not much to do yourself though.