I think that unless they're ultra low mileage or in as new condition you need to be looking at the pinnacle vehicle for each type which would probably mean going over your budget, if looking at R129 Mercedes SL's you should be looking at SL600, SL60 AMG or SL73's as SL500's are ten a penny, if looking at a Corrado then it would need to be the G60 version etc. I'd steer clear of the BMW 8-series as they have multiple problems with electrics, the E36 M3 is worth looking into but again not at your price point. If looking at Impreza's then it would need to be a P1 or RB5 version.
The cars i'd be looking at would be things like Peugeot 106 & 306 Rallye's, Renault 5 GT Turbo's and Ford Racing Puma.