Congratulations on seeing the light
Obviously most of us on here will have a certain amount of bias towards the nsr I think as Andy said the nsr is probably the best choice of the 250 2 strokes and you wont regret buying one.
Spares are easy enough to source in the internet age as lomg as you dont expect to walk into your local shop and buy them off the shelf. I use Lings, David Silvers and Jap4performance in the u.k..
As you said if you are buying a bike of this age you must expect to spend some money and do a cetain amount of work, even Rich G who bought his imaculate Rothmans SP from a dealer has had to rectify a few problems since he bought it.
Here are a few buying tips from a previous post:
Make sure the powervalves work! If not cleaned they seize up, burn out the p/v servo and then burn out the pgm unit.
Take the r/h quick release fairing panel off, the pulleys on the side of the barrell should open and close at about 2-3000 rpm. You should be able to rotate them by hand as well, 2nd hand pgm's generally sell fo £100 to £150 when they OCCASIONALLY come up for sale.
Cold starting issues tend to mean the crank seals are shot.
The pistons last a good few thousand miles, I just changed mine at about 6000 miles recently and the pistons were just out of limit. If the seller cant tell you when the top end was last done try and bid him down the cost of a rebuild (£170 from Jap 4 performance).
You havent stated wether its an R, SE or SP? I guess you have read the model history on this sight, SP's are obviously the most sort after and should have adjustable forks, remote reservoir suspension, dry clutch and magteks (smooth rim with no lip, magtek on the spokes)
Good original bodywork is as rare as rocking horse sh*t and in my opinion is well worth paying extra for, but it depends what you intend to do with the bike.