Stock brakes are fine unless your spending time on track. I ran 420hp on stock disks and pads.
As Danny says though, the only real option is the GTM kit. I know that HKS developed a kit for the HR but I don't believe it was ever released. Your best option is to contact Abbey - I'm pretty certain they can supply the GTM kit and they will fit it aswell
As for cost, I reckon you would do well to do it all for less than £10K