Check the regular places like KBB, EDMUNDS, NADA. They built these cars in such large numbers that there is no exclusivity. No reason to pay a premium for this one if, for the same money, you can find a newer one with more features (at least if they are features you want)
IIRC, 1997 were not "issued" to run 18" wheels. Not till 1998 when Porsche upgraded the suspension were 18"s "allowed", per the factory.
Wholesale prices are likely in the $9-11K range. Retail should be in the $12-14K range, imho.
These are not "necessary" type cars. With fall and winter approaching, prices for convertibles will drop. Wait till spring though, and you will likely pay more
