Get a recharge kit from an auto parts store. They are usually around $40. It comes with all the fittings, hose, oil, and r-134a freon you will need.
I'd start with a leak test kit. Obviously it leaked out somewhere. Look under your front bumper and make sure your condensor (looks like a radiator) isn't busted up. Then look behind your throttle body at the accumulator and make sure its not cracked. Run some leak test through it, and it should kick the compressor on for a few seconds when it takes a charge. Then you will see a red dye seeping out through any leaks in the system.
If all is good, use the recharge kit. The compressor has a safety switch that won't kick it on if there is no freon in the system otherwise it can burn itself up. So to tell if its working you'll need to fill the system.
Price check? Well you can get the complete unit or just the clutch assembly. I don't know a price off the top of my head, call an auto parts store and ask them.