few things to do mate.. i assume its v6
replace air filter with pod filter (check legality in your state) -$35 cheapo
replace spark plugs with higher conducting plugs - $35 - $50
replace coil pack with VP-VT coil pack (way better spark) - (Ebay $60-$150) ive seen
replace ignition leads - $20 - $30 is good
2 1/2 sports exhaust (redback have a nice note) - $200 - $250 is reasonable
change engine oil and transmission oil (huge difference) - $40
put a few mothballs in your fuel each time you fill up - $2 (HI OCTANE BOOST!) im serious...
another thing i found was brilliant to do, and FREE, was pull the manifold off the motor, and clean the bugger out PROPERLY, and re-seal it TIGHT. engine response is much better..
thats your entry level mods for a vn.. you can have a fully serviced well oiled smooth driving MEAN sounding vn commodore for around 400-500 bux depending on ya bargaining skills.
wanna go a little harder? look at camshaft and chip packages from crowcams
diff gears 3.75 4.11 etc maybe even a stroker kit (v6's are available now) engine rebuilds with port n polish, shave the heads, gearbox shifters, higher injectors and harder pumps.. few things that'd cost a few thousand but you'd embarrass a few v8's out there
check out FIT if your budgets as big as your eyes, get a turbo manifold kit, intercooler and associated plumbing for your VN v6 for about 7,000 i think,
you sort it out mate