ROFL, I have one smaller than my pinky sittting out in the rain. poor little RS sway bar.... You can get Cusco 22mm rears for around 165 shipped, 3 way adjustable. Just make sure you replace the plastic endlinks and the sway bar mounts or they will die in no time.
The plastic endlinks are fine, as are the mounts for any bar under 25mm. It will improve the handling to upgrade the links, but it is not necessary. If you go over a 25mm rear bar- then the mounts will break. Up until that point they are strong enough to handle the stress of the bar.
also you can get a whiteline bar for less. And a helix one for even less. Its a bent piece of metal, they all work the same, I would avoid paying the extra to cusco for their name
If you're interested contact Tougetuning on RS25.com he's got some great deals on Group A solid endlinks for subarus right now (~180$ for all for)