when you say interior im assuming you also mean sound deadenind material?? that and you could get crazy.. EVERYTHIGN adds up.. windshield washer resv and windshield wiper motor and mech... lexan windows (kinda costly) cheap plastic summit racing seats.. they are realy uncomfortable but light as hell... C/F hoof.. fiberglass door panels and fenders... A/C if you have it... i mean like i said it really depends on how rediculous you wanna get... swap dash board out in favor of some aluminum sheet metal... headliner... your goal will not come easy. what EXACTLY is it stock??