The reason so much is spent on the V8s is one, its ultra competitve and teams with the cash will spend it to gain the extra 10th of a second, and racing componentry is massively expensive. Road car mods are cheap as chips compared to what a race team spends. The brakes, gearbox, and shocks in one of our V8 supercars is worth more than my whole modded 32GTR owes me (and its a lot). Id luv to write out a price list here to give peeps an idea but i wont....most of you would sht yourselfs at the costs and it would change you whole perspective on the cost of your road cars mods.
A more relevant comparison would be to compare the new GTR to other expensive road/race cars...id luv to see a 07 GTR in the GT champoinship next year to compare it to the Lambo's and Ferrari's and Porsche's...but I dont think that will happen any time soon