Din, no thanks man... the rear bumper does not fit onto a 4-door!
Satigue, the price depends very much on the route you take. For example you could go the cheaper way and modify the hoodlock and hinges and use a standard metal bonnet, or you could change all the parts for new ones (GTR ones) and go for a carbon bonnet which will cost a lot more. I suppose it could be as cheap as RM1500 or so, and as much as you'd like to imagine!