You can fit an adjustable cam pulley on the exhaust cam and get it dialled in and that should give you a gain of somewhere around 10bhp. You can get that done for under £300, speak to Torque of the Devil. A remap will help too but won't give you the same gain for your money.

What was said earlier (and taken the piss out of) is kind of true, there aren't huge gains to be had from the normal tuning routes as they're already very well tuned - induction, exhaust etc, even the standard cams are pretty lairy.