I disagree with your disdain for 0% interest deals. Mostly because I have one running right now. I'm paying the minimum payment to the store and saving the remainder in an investment account until a month or two before the deferred interest kicks in. I've only earned $13 on what I've set aside so far (which is actually 4.7%, but it's a tiny principal.) but that's better than $0. The only caveat you made that I may concede is that people may spend more if they're offered 0%, but that seems subjective. I had a professor that told us, "Be fast to take money in and slow to pay money out." (all else being equal, which I think 0% equalizes things a bit)
I would certainly never refer to the price of an item as, "$x per month," though. That's barbaric.