You might find this interesting, it's not THAT different.
NISSAN GT-R 3.8 V6 BLACK EDITION GTR ~ LITCHFIELD STAGE 4 | eBay
If I am honest it seems a little cheap to me.
I'd expect your car to be worth about £38k or so myself, particularly with the suspension kit that is about £4,200 (IIRC?) supplied and fitted.