just a down pipe realistically, the cats the restricitive bit, about £500 for performance downpipe and cat, but you could always get a de-cat downpipe for a lot less pipewerx do a 3" De-cat DP for £265. add your £50 for the revo upgrade to stage 2
so for £315 you could be pushing out nother 30hp now thats value for money. this is the reason the k04 engine is the way forward for tuning