Michigan: You have to file papers with a magistrate when the car is sold anyway, so you just pay for the temp tag there.
North Carolina: Dealer took care of it for me, but it was just a matter of paying $20 + proof of ownership and insurance. I faxed the sales guy I was working with my insurance info and drivers license and he had the temp tag waiting for me when my plane landed.
Those are the two states I’ve had temp tags from. Guessing it’s the same everywhere. Google is your friend.