well ....
SC and TC will run you about 4-8k like you said
and a shop in NY i hear has been doing S54 swaps for about $6500 (if you were to do this yourself it would be an extreme amount of work)
http://forum.e46fanatics.com/showthr...ite46+s54+swap
I would say Twin screw SC, i havent heard much on turbo charging the E46
and besides
Headers
Sharking
Exhaust
CAI
(which you would do all of these anyways with the SC or TC, minus the sharking)
there is not much more power to be had in these cars without Forced Induction