My recipe for a quick car on a $25k budget
A nice R32 GTS-T for about $13-15k
then spend the rest on:
RB30DET
aftermarket turbo/intercooler/piping/cold air
RB25 Gearbox
clutch + suspension upgrade
decent tyres
If you've got anything left, which depends how far you want to go with those things, then you can look at other mods/accessories.
A reliable powerful car costs money, and it's pretty hard to get there on a $25k budget, unless you buy a car that's already modified, and then you run the gauntlet with reliability.
Also, beware of the late model commodore and falcon - the LS1 and the XR6T are easy to get power out of for a little money, and there are a few cars here in SA with big dollar builds that can run some pretty serious numbers.
All in all, have fun with your car.
Keep it safe - we'd hate to hear of anything bad happening to you.
chops