It's almost certainly a coolant leak, but it might not be. Pop the hood and start the car. See if the compressor is working, or if the pulley is just spinning and the compressor isn't doing anything. If the compressor appears to be working, you probably have a simple issue with a vent system door not opening or some such. However it's probably an a/c refrigerant leak. If that's the case, you are indeed right to be worried. I would not have the dealer fix this as their rates tend to be very high, on the lighter side they have the right equipment. A dedicated a/c place would also have the right equipment with hopefully lower rates. A good indie mechanic, too, should be set up to fix this. 

Air conditioning is big bucks to fix, most of the time, as you fear. However, Toyota "might" stand behind it since the car is still practically new, and the dealership "might" cut the price because the car might have had that problem when they sold it to you.