What u gotta understand is that its not as cheap as it sounds.
So okay u do the turbo mod for 350 bucks.
On a RB20, u will need to upgrade: Clutch, very expenisve, Internals, as Rb20 cant take as much power as rb25, Gearbox as rb20 g/box is prone to failure at higher power levels, upgraded fuel supply, and then a retune of ur ecu.
Probably about 5g worth for it on a rb20.