How much would a mint condtion 1990 mx5 with 18,000 miles sell for?

I would guess between $6500 and $9000 dedending on condition and maintenance. I would also say it would be on the lower end if it was red or white car versus a mariner blue. I would check two places for value #1: hemmengs motor news has done a great job on bringing these cars vaule it light. #2: miata.net ( pricing and dealer disscusion ) which you will have to become a member to post your question.

Also if it came with a factory hardtop it car add an extra $1000 to $1500 added value.