Will your local gas supplier fill it? I would make sure first! I would price it out from the local welding supply. See what they are charging. Might be worth it to go up a size? The bigger the bottle the cheaper it is!
I've seen used 20cf cylinders on ebay for a little bit cheaper, but not much. If your local gas supplier only does exchanges, I would keep an eye out for a used one rather than buy a new one.