As always, start simple. Sounds like your AC needs to be recharged. A simple Google search will turn up all sorts of how-to instructions on doing this. If you recharge the system and you wind up back with no AC again in what seems a short time, you likely have a leak in the system that you're going to need to track down.
I have talked to two shops and both refused unless they could do what they called a full workup starting at $149 at the dealer. Plus the cost of freon.
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