the only things that will add noticible power is turbo and changed headers and the whole exhaust piping, you can buy all that on ebay, but have to be very careful, you get what you pay.
to add some noise just buy a muffler (which will not add power without bigger piping and headers)or buy a cheap short ram intake, i have it, and love it, it gives a nice deep sound, some cai piping from ebay are sometimes not bend for proper fit.