LOL @ anyone modding their Subaru's. Good luck. Depending on what stage you go to, I'll place a bet on when your engine spins a rod bearing.
This is the kind of insanity that comes out of those communities. Visit Subaru boards. One such thread warns not to "push it in a low gear while driving uphill". Wow. Pretty much sums up the price difference.
Also, with regard to modding, if you actually do it properly, you will be in M3 territory cost-wise, except the M3 will have warranty and won't blow up.