I did a "whatif" on Progressive's page for changing my 97 Prelude to a 97 M3 coupe. It went up $450 for me
Anyway, the Prelude is one of the more expensive cars to insure, supposedly. There was a "cars with the top 10 insurance premiums" list released a few weeks ago which I saw on Edmunds. They had a note on bottom saying if the Prelude and Integra were still being made, they'd have been on the list.