The dealership wants $119 for this service. This is something I can do myself, right? I believe it's just a Freon or something of that sort with the added benefit of killing mold and keeping the car smelling new (as they put it)
Short answer - are you having problems with the A/C? If not, skip it.
Back in the day when cars took lbs. of Freon it was pretty easy to just dump a can in there when the A/C wasn't feeling as cold. Today the cars take oz. of refrigerant and it's a little more complicated because, if you overfill the system, it actually doesn't cool as well. So the way a shop should be doing it is to completely evacuate the system and then put in the exact quantity that the system call for. The mold thing is a different story. They need to gain access to the evaporator and spray a cleaning agent on it and the rinse. If the dealer is going to do all the above for $119, it's a bargain. If all they are going to do is measure the A/C presures, possibly add a bit to get them in range, and spray some Lysol down the air intake grills, then it's not.