If you guys are looking for a used one on CL make sure the date is still good because they only last 5 years before you have to take it back in for the test which is gonna cost you about $35-$40 so may as well buy a new one for $57 which will last you for 5 full years
I spoke with someone at Roberts Oxygen (they have lots of locations around the baltimore area) and they swap tanks for $21+tax a pop. Seems like its worth it since a refill in the area goes for about $15 if you have your own tank.
Yeah I think you are better off buying a new one ,its nice and clean and not nasty like the one Robert oxygen gives you ,and you can go to peevs paintball to filled for $21 ,,Robert oxygen only opens on weekdays.
I'd normally say local is the best bet for 5lbs, but that Amazon price is pretty good.
One other thing to keep in mind, if you're up for something a bit larger - beverage elements has a repainted, fresh hydrotest steel 20lb for $90 shipped, and finding a better deal than that will take some doing.