My first thought is to get to a hardware store, buy a pair of bolt cutters and get that collar off of him, I'm sure it's not helping his breathing, which will make him even more scared. My little Ace Hardware would probably just cut it off for me and spare me the $25 to buy them.
I hope the vet is wrong and it's something that can be taken care of quickly.
I'd also drop that ER a note and thank them, then send the bill back to the other vet and tell them where to stick it.
Please keep us updated.

