You will never get an S14 or S14a for under £1000 unless you know some people. S14 maybe... but your talking high miles and probably very ropey. If it's on std suspension it's gonna be knackered by that age. I can tell you right now.. if you own a 200sx it WILL cost you money, purely down to you wanting to improve things. Suspension/arb's + locking collars will help immensely, but don't take the pee else the RWD will bite you in the arse.
And Stage 1.. what the heck are you on about man... if it's got stg1 already (As defined by Horsham developments and generally accepted), its probably gonna cost at least £1500 if not £1.8k+ for an S14. S14a.. no chance you fruitcake lol.
S13 (pop-up lights), you will be able to get pretty easily for under £1000, but you will have to try and get a good one, otherwise you'll hit problems. Once again.. you'll want to pump money into it. On higher milage cars, big-ends can go if not maintained well, and Stg1 will only get you to about 220bhpish as it has a smaller 1.8 engine. Stg2 will get you the equivalent (almost) of the stg1 s14. Overall, I would honestly not suggest getting a 200sx for only a grand (even though I did with my S13). (I have also owned an s14a bought for 4.7k and spent 3.5k on mods in one year). Unless your prepared to spend some cash on a 200sx don't bother. (Should say that for an S13 you'll be looking at least £2k for decent 'raw' car).
MR2.. try and get the non t-bar model, as it is a better chassis

Mk1's are cool. Don't try and get a mk2 mr2 Rev 1 unless you know about them. They are easy to crash if not experienced with the way they let go. Good car and defo in the category for buy. I would happily own a mk1
205gti is good suggestion if you can find a good one. (watch for lift off over-steer

)
Pain in the arse to work on and some common probs, but a clio 1.8 16v. Fantastic handling.. just take your time in getting a good one.
Also.. take a look at some of the Saab turbo's, they are a LOT of car for the money nowadays and can be picked up cheaply.