From everything I've seen (including unsuccessfully trying first-hand to remove just the clutch assembly), Fozzies from these later model years do not have a separately replaceable A/C clutch, so you have to go with either a new or remanufactured unit that includes a clutch. Should be looking at around $270-400 depending on your source and brand.
Replacing the whole thing CAN be done somewhat quickly DIY, assuming you know what you're doing and can get the refrigerant lines drawn down at a properly equipped local shop before starting work.
But it's also worth your time seeing if Subaru HQ 1-800-SUBARU-3 would be willing to cover the cost of replacement (which they SHOULD if your vehicle is under warrant, and MIGHT if you ask real nice and/or politely reject a legit quote from your dealer's service center). Cite TSB 10-84-16R as reference.
Otherwise, you're looking at a $750+ job.