Your cheapest route is to sell the N/A and buy a TII. Period. Any swap is going to cost you more than just buying the car you need to start with.

If you are dead set on keeping it cheap, and staying with the car you have, shoot a small N2O shot on it. No more than 50 shot to start with. That will get you to around 200 flywheel hp - assuming you are stock now.
If you go higher, you will probably start breaking things like your tranny, or rearend.