check for a loud ticking coming from the engine, can point to the head gasket being knackered, and the oil and water very rarely mixes when the HG does goes, as it doesnt go in the same place as normal cars, so checking for the oil and water mixing wont help. BUT, they tick when the exhaust manifold gasket goes aswel, so if it does tick, dont just assume its the HG, could be the EMG, so do further investigation, like does it over heat etc.

make sure at around 3k you get a big pick up in power, if not, the IMRC is knackered.

they go through bottom arms pretty quick, so check those. the arms on the 200 are expensive as there specific to the 200, £100+ per side, where as 24 arms are cheap as chips

check extensivly for rust, ive known cars with zero rust on the top side, and look mint, be wrotten as a pear on the chassis legs, floor, and sills.

as for 24 v 200, the 200 is the better car, better spec, quicker etc, but with your budget, you will get a very nice 24, but only an average 200, although the prices for 200's is rock bottom at the minute, so you might strike it lucky if you look about, ive seen a couple of decent looking one's for around £1500 in the last few weeks