Lotus Exige! Dave Struve in used them, they look great and are super comfy. They do fetch ~1000 pounds on ebay usually though...
MX-5 seats need some trimming of foam and metal to fit the Locost chassis, perhaps they will just fit inside Haynes if you just remove the reclining mechanism.
http://www.cheapsportscar.net/diary.php?UID=207