987 Cayman S, gen 2 if you can stretch it. Gen 2s have a much improved engine over the earlier models although a lot of gen1s have had rebuilds and upgraded IMS bearings now. Bought mine April last year and sold in August and made about ยฃ4k even after putting 6k miles on the thing and a track day. All petrol heads need a porsche at one point I think.
If budget is a bit less I'd have a Z4M, arguably a more "lively" engine than the Porsche but less balanced and more tail happy and is more likely to keep you on your toes when pushing on. Proper M car with a short ratio 6 speed, quick steering rack, mechanical diff and a accelerator pedal feeling like it is glued to your foot. Can still pick a nice roadster up for ยฃ16k would be my choice especially with summer coming up.
If you want something a bit newer and with a turbo Z4 35i all day. Simple mods and a tune can have 420bhp and 600nm of torque in tap. A folding hard top, making the car feel more like a coupe and all the mod cons you need inside. Not quite as much of a drivers car due to the lack of the responsive NA engine and hydraulic steering but still a good fun and very fast car!