First option is get yourself some braded steel brake lines, goodridge make some top quality ones. Will cost approx 70euro.
Upgrade your fluid to Dot 5 and get some grooved discs if you can stretch this far.
Next option would be to find a second hand set of STI 4 pots and discs off a classic sti. Approx 3- 350euro
Next option is get some second hand Brembo calipers and discs off a new age(bug or blob eye) impreza. Approx 5 or 600euro. But you'll need 17inch wheels or bigger. And some 17inch wheels will not clear caliper.
Then to go all out for maximum stopping power, Get a big brake kit which will include grooved discs and new huge calipers and fast road pads. Again you'll need 17inch wheels or bigger and these will cost upwards of 900euro.
Ap racing are supposed to be the best. K sport, Stoptech, Tarrox, Brembo are a few of the makes available