1996 Subaru Impreza Only blows hot air

This happened all of a sudden...
I live in L.A. And use either the "vent" or "A/C" to get cold air inside my car. I worked late one night last week and it got quite cold, so I turned on the heat for a good 20 minutes. The next day I drove the car and noticed that no matter what selection I was on (vent, A/C, etc.) And no matter what air temp. Selection I was on (from as cold to as hot as it gets), I was only getting hot air. I've kept an eye on the engine temp. Guage and it's not doing anything different - staying pretty much just below the half-way point. A friend told me that maybe my A/C system died, which seems logical as there's no more cooled air. Can someone verify this, or suggest what else it could be? Also, don't suppose you know what the average cost to fix it might be...?
Thanks,
~C