if you keep your 2.0 look att bbm, they make a nice supercharger, or kinetic motorsports for a turbo
if you go vr, you can find a doner car for under 1500. You will need engine, trans, ecu, wiring, axels, and subframe.
If you want to go 1.8t, its not as hard and expensive as people think. You can use your stock trans, ecu, wiring, and everything if you get the chip and kit from reflex tuning. You will have to do some small things like run 16v plugs, but not much. You can pick up the used engine for about 1k and get a custom exhaust for under 500.
If you have any questions or need further info ask, as i have done both vr and 1.8t swaps in mkIII's