A cheap repair of sorts is, you can but top up cans of A/C gas which will tell you if the system itself is working if you then get cold air. IF, the cold air doesn't last long then you have a leak on the system. To diagnose that you need a proper Re-Gas where they would add a Dye or use dyed gas. Any leaks can then be seen using UV light and special glasses.
Tony.
ps. Turn temp. control to minimum, press A/C switch, turn blower up and you should have cold air.