You can always lease a bottle of most any kind from your local welding supply. But regardless of how often you use the welder,you will still be billed on a regular basis for the use of the bottle. I've found the best way to go is to purchase the bottle. That way if you don't use it for a period of time there is no expense other than the cost of the gas.
Also unless you are planning on welding aluminum, CO2 will work just about as good as Argon or the Argon/Co2 Steel mix gas. And it is normaly much cheaper than pure Argon. I have 2, Co2 bottles that I use for mig welding and they both came from a soft drink machine. They have the same connection as the regulator on the mig welder and they cost me next to nothing. I exchange them with the welding supply when I need to have them refilled and never have to worry about paying for the cost of testing the bottle that way.
I also have a regular Argon bottle that I use strictly for tig welding, that isn't used very much. I normally have it refilled about twice a year and don't have to pay rental fees on it either, but it is always there when I need it.