Humphries no longer leases tanks. Bruce told me they lost a lot of tanks at the end of a lease period since people had nothing invested. They do rent them short term though, but for that you put up a deposit for the full amount of the cost of the tank. The main thing with a purchased tank is to make sure your swap does not have a company name stamped in the neck ring which indicates store owned. Having a name painted on the side means nothing. Mine currently have a name on the ring, but Bruce said they keep track in the computer since I bought them there. If I ever leave the area, he said they will swap for ones with a blank ring.
As for as cost of gas, go big on the tank since most of the cost of a refill is the labor. Refill on my 120cf argon was $80 but only $85 on the 200cf. Also figure in your time and effort to go do the swap.