(one) would be lucky

That is very unlikely to happen or be the case. The phrase is used sarcastically or with a sense of resignation. And just who is going to pay me back for this thing now? I'd be lucky if I get 50 bucks for it at a pawn shop! In my experience, anyone calling a government office would be lucky to get a live person within 30 minutes. I've heard Mrs. Smith's exams are notoriously hard—like, we would be lucky to even pass, that hard.