AC Recharge - 300D

[littlerobot]

I've just replaced all the diaphragms in the vacuum actuators under the dash, so now my climate control buttons open and close the proper vents. The car (300d) sat in my garage for a year without being regularly driven. The AC worked great before it sat. Now the air isn't cold. My instinct is to take it to a garage for a vac and charge, but that is over 100 dollars, while the canned stuff at the auto supply is 20 dollars. My question is, If I get the 100 dollar vac and charge and it doesn't work (because of a leak or who knows?) then I've wasted 100 dollars. If I get the can and it doesn't work, I'm only out 20 dollars. However, if the AC does get colder, then I can be sure the system works and then take it in for a vac and charge. Is this the right logic and the best way to proceed?