The cost to do the conversion isn't cheap. Though your set up for higher power than BPU once you lower compression, your limited by transmission woes, so it just doesn't work out cheaper.
Buying cheap parts like manifolds won't matter, welding a manifold won't break the bank but getting decent parts like a good ECU and return lines make everything add up quickly.
Don't forget, you can get a turbo on an NA cheap, but if you don't buy all the supporting modifications its pointless. My clutch + flywheel cost me £670, thats just ONE example of a conversion cost that people don't often talk about, when I had everything installed from a completed shopping list, I had another £400 in parts like intake pipe, manifold bolts etc etc so theres 1k instantly to your budget that no standard NA-T kit or shopping list will give you.
Don't forget cheap kits WONT include ECU Clutch Intercooler OilCooler.... Best to go TT or spend a year doing ur research and peice your own kit together.