Some vehicles are known to leak a little bit of freon over the years (possibly an oz/year). They should have told you how bad the leak was. If it holds pressure/vacuum for 30 mins or so I'd just re-charge it and throw some dye in it if possible. I wouldn't be surprised if they had trouble finding any leaks and just blamed it on the evaporator.
Autozone might have an a/c manifold gauge set and a vacuum pump available for loan. It'll cost you $300+ but you get your money back when you return their stuff. It's not hard to learn how to service your own a/c if you think you're up for it, just don't attempt to use one of those single hose with a gauge filler'up on the low pressure side crap they sell, that won't turn out well.
Walmart sells freon (super-tech) here for about $5.90 a can.
In fact I want to say most vehicles leak at least a tiny bit because the systems aren't 100% perfectly sealed, and that's why we have driers/accumulators to deal with anything that does get in, as long as it isn't too large. That's my understanding at any rate. So for old vehicles, they may get low on freon over time, but shops want to make the beans, so they'll find something to blame it on.
Last edited by dhath81; 06-07-2019 at 06:46 PM.