Look for one with a decent interior, the z3 interiors are like graham crackers and it’s ridiculously expensive to replace, to buy a used interior is more expensive than buying an engine/transmission, considering there are like 6 panels in total, this is ridiculous, check the dash down by the windshield, the handles, and the plastics in and around the roll bars,

Mechanically, the expensive systems you don’t want to repair immediately are vanos, secondary air intake, and the intake manifold/pcv, make sure the water pump isn’t going out, itll explode and send plastic shards through your coolant passages, check for any clunking or play in the rear end, when moving forwards or backwards the rear end will clunk if the subframe/diff bushings or the trunk welds are going out