Could always try a diff back if you just want a bit more sound, shouldn't cost more than $300 to $400 (depending on material choice for muffler, e.g. stainless steel verses steel), won't be as loud or as deep as the cat back.
You could also go down the path of
TBE/retune but this will blow the budget.
Factor $1000 minimum for a
TBE and at least $1100 minimum for a retune.
This was a
retune of another members MY08 WRX.