Not sure but I’d go for more “modern” and less “classic” at the moment. Classic cars seem to be in a bit of a bubble currently, prices have shot up for a lot of usable classic sports cars over the past 5-10 years. The bubble might not burst, but prices are already quite high.
Buy something you would like to own, at least then you’ll enjoy it and if it ends up worthless it’s not so bad. Unless you are very skilled in the workshop, find a good specialist to look after it if you are going to keep it long enough to appreciate significantly. You’ll probably spend far more than you will ever make.
I would guess Elise S1, possibly Mk 5 golf GTI and R32, and (although maybe above your price range currently) almost definitely the V8 M3s – probably the latter more so, as they were really under-rated when launched, being heavier, “less focussed” etc., but having been in a couple they are very nice cars and have plenty of performance, plus being last of the naturally aspirated era are likely to become desirable (whether you are a believer in turbocharging or not the “end of era” cars always end up going up in value).