1500 not really that much, but i would go for 4 branch manifold, induction kit, full exhaust system and decat. this give really good power to engine(10-15bhp). intake manifold also good if you have money left over
Your budget is not the only thing we need to know.
1.) What do you want? More top end, more torque low down, more overall power
2.) Only engine mods or gearbox also
3.) What have you researched yourself
4.) What are the mods you have done so far
Aftermarket cams and a mapped ecu. Or as jdm 3383 recommended, a final drive kit for your gearbox.