From what I know and heard, that getting 300whp on Wrx is posibble for about 8grand that is.
Parts:
Full exhaust - header -back 2,500 varies by brand you get.
Fuel Injectors -450
Fuel Rails - 350
Fuel Pump - 100
Your Choice of Turbo - 1,500 or less
TMIC or FMIC - average 1,000
Engine Management - Element/Hydra or Eutek ECU piggy back - 1,000 ,1500
DYNO Tuning - about 3-4hrs. varies by dyno shop.
I might of missed something, but a 300+whp on paper = priceless