I got mine from Airgas today for $95 filled. That was the cost for the initial tank plus the hydro test? I think thats the name. Anyways, when the tank is empty you bring it back and exchange it for a new tank and pay $18 for the refill and test again. I know it's cheaper to just get the same tank filled over and over, then have it inspected every few years but I don't have that option where I live.
I know they only give out aluminum tanks, so that is a huge bonus! Oh, and don't bother with Norco. They are more expensive then airgas. It seems like most cities either have one or the other, or both.
These items vary from place to place but I think there is some misunderstanding here. I think what you will find is that you do NOT take it back and get a new one. If you are doing a swap, rather than a refill, you are likely to get a tank which is part of their stock tanks. That means it is likely to be one which has gone out numerous construction sites and ridden around in trucks much of the time. To keep tanks from "wandering" off, they are often marked or painted so they can be recognized.
Just a heads-up so that you don't expect to get a shiny new tank each time when exchanging. Locally, the deal on exchanges is that you leave your tank on the dock, pay for the gas and pick one up as you leave. Pot luck on what you get but my folks are nice enough to let me choose nicer over rusty.