Cats pant like that when they are distressed (from that video on first page). If you're calling a local shelter (one that doesn't euthanize preferably), see if they can scan for a chip (make sure its not someone's pet), let them take care of it either way and if no owner is found (check with neighbors too) someone can adopt it. I had a cat get loose from a neighbor once and I took care of it for a day since it was hungry, until I found whose it was then gave it back. It was a trained cat though in my scenario.
Antihistamines are pretty cheap. You can get like, a months supply for about a pound. I do appreciate your attempt to put some realistic grounding on the matter though, but I'm always going to be in favour of living the kitty dream!