im after some knowledge on what performance parts will give some extra power but not blow the budget[/b]

crow cams we had crow cams in a 260 and got 40 kw more

Get a Flash Tune, good induction and full free flowing exhaust. This will make a world of difference. If you can afford it a set of 3.73:1 or 3.9:1 diff gears will give the car strong acceleration and will help the engine with all that weight it's gotta haul~ Basically any performance shop can help you, there are loads of performance options for the XR8..

IMO the best bang for buck on these engines is any type of forced induction.... Centrifugal blower...

CAI - bluepower/g&d, ss inductions and similar crap offer very little gains, maybe 4-5rwkw
$600

Exhausts - I prefer di filippo but each to their own
$2,000-3,500

Capa flash tune - custom tune
$1500

5 speed man - 3.73lsd/high performance clutch
6 speed man - 4.10lsd/high performance clutch
auto - 4.10lsd/3000 hi stall
$1900 lsd/$1500 or so, hi stall

Underdrives pulley
$350ish

Don't bother with a larger throttlebody, does not make a difference unless you want an extra tenth of a second down the qtr. They also play up alot

I wouldnt bother with cams until all that is done, the car will need to be tuned after and to get the most out of a tune you should have the exhaust and cai done.