Here u go heres some pics of my first MX bike a 1994 YAM 250, pretty quick for its age, i just stuck a new piston and rings init, decals and new seat cover, and cleaned it up a bit, it's also got a kawasaki KX front number plate since the yam one's where ugly.
I bought it for £850, done it up
I had the front forks re-sealed, back shock fixed (leaking), fixed all the slop in the suspention bearings. spent a load of money on it. bloody thing was well unrealiable,
3 gears went in the gear box, fixed that with new parts and then 2 of them went, eventurly fixed that. then the bloody Con-rod snapped and went though the barrle, i repaired this with a new barrle, Conrod kit, Piston kit. and sold it for £900 after having it for a year, but it was a much better bike when i sold it, the bloke who tested it said he had tested 5 bike already from that year and my was the best condition and i was the fastest, but then i stripped it down and resprayed the fram, ECT for i sold it.
So this is the kinda thing u should be look ing out for,
1990-1994, Kx good but ugly, Yam good and good looking, suzuki shit and ugly, honda good and ok looks
1994-1998 honda very good and good looks, yam still good with good looks but suspention not the best, suzuki still not the best but lookin better, kawasaki looking a lot better still realialbe and good. 1998+ Kawasaki look very nice and very realibalbe, honda lost their handling with the alloy frame from 1997- 1999 and their 2 strokes where gutless from 1999-2002, Suzuki pretty good, and they look ok, yam suspention got better from 2000+ and their engine got more reliable aswell
Hope this helps if i was u i would get a 1994 yam or a 1996 honda 250 but obviouly get a bike on condition not make.