Around £4k or so seems to be what people expect for a v-tidy '28, Lobelow asked £4.5k for his, don't know if he got it though.
The value of anything is just what someone will pay for it, after all little antique trinkets actually worth near nothing fetch tens of thousands at auction.
I'd worry* more about if it's all there and o.e. Honda than if it's mechanically perfect if you're after a minter, engines are easily fixed, swapped out or whatever and, shiney or not, if you use it then it's going to go wrong. But getting hold of perfect mc28 bodywork is either a very expensive or very difficult process and as stocks run out it'll become both.
You can't be bitten that hard by a 250, you could easily buy what appeared to be a nice RC30 or '45 and find yourself with a job few would attempt at home and a repair bill running into 5 figures. There isn't such a thing as a NSR250 rebuild people on here won't talk you though and if you do the work yourself and have a bit of patience you'll really struggle to get into 4 figures (GBP).
But you won't get a '28 real cheap these days, I paid £1665 for a non runner with no bodywork to speak of. If you just want a 2 stroke that sort of ££ will buy you a decent mc21, a good Aprilia RS250, a very good RGV vj22, a mint RGV250 vj21 etc. But if it must be a mc28 then it must, only you know if something 2nd class will do.
*I wouldn't "worry" at all, when all is said and done it's a 10 year old motorbike, the world won't end no matter what is wrong with it.
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