Get a used Miata. A blast to drive and very reliable. They are not easy to find and they always command premium prices.
My oldest son has a Jeep for summer/weekend driving.
Any 10+ year old Porsche or Mercedes can end up being costly in maintenance and repairs, even if you barely drive it.
Also, I don't know about where you live but where I live, sports car are a tough sell during the autumn or winter months. They sell faster ( and usually for more money ) in the spring when there is a higher demand for them.
Hi prestige cars of this age usually needs lots spending on them to even drive . a normal sports car like a old triumph spitfire would be less expensive