The kit especially if it's the tuner one is basically all the bits you need from GTM to get your S/C build underway.
On top of this you need a fuel return system,bigger injectors,hybrid oil filter kit,bigger fuel pump,oil cooler,baffled high capacity sump(if you don't want to do a Grundy),complete new exhaust system to allow the engine to breath and an up rated clutch.
This list is a minimal as once your running big power all of a sudden things like brakes,suspension,diff and tyres feel totally inadequate.
Oh and I forgot to say that you have to pay someone to fit this little lot and tune the car afterwards so maybe you can see why the money can add up quite quickly.