Your best bang for the buck with be the Kartboy short shifter, and Tom is actually a sponsor here.
If you just want a shorter throw, you'll only need the shifter itself. If you'd like to firm things up a bit, get the front and rear shifter bushings while you're at it. Since you've got a MY04 the rear shifter bushing will work on yours, unlike on the MY06-08's where it doesn't fit properly.
If you'd like to make your shifter feel AMAZING... get the Subaru Group N 5-speed transmission mount. It'll be like night and day difference in the shifter feel, but won't be very amateur friendly with the shifts.