a decent cold air intake like AEM a good flowing header and an exhaust will be best to start with. from there you can add things like test pipe short shifter clutch/flywheel cams and adjustable gears and then on to bigger things.

my brother has a spoon axle back (there is no rear axle but hey) exhaust for sale. combine that with an ITR b-pipe (pipe from cat to axle) and it will flow pretty good. he also has an AEM cold air intake for sale soon as soon as he gets some bolts to put his stock unit back on.

also if youre looking for something fun and cheap you can remove the stock airbox and just run the stock or a K&N cone filter for a little bit of gain but nothing you will feel. just gonna be louder