[Triple Jim]

The 90 cubic foot tanks are the best deal for me, now that I'm not welding daily. I own a couple so there's no rental charge, but the welding suppliers will swap them when I run one empty so I don't have to get them tested. 90 is the largest one they'll do that with. I used to have a 300, but it was $80/year rental on top of the cost of the gas. If you're not using it very quickly, it ends up costing more than owning a couple small tanks.

You can get away with owning one tank, but I prefer to use one up, change tanks, and swap the empty one at my convenience, rather than having one run out and stop my work until I can get a full tank. The suppliers will sell you a tank, but I don't know if you can buy empty tanks cheaper and get them filled. If you try to go that route, before you buy a tank, ask your supplier if he'll swap it. Some won't if you didn't buy it from them, so you have to drop it off, wait a week, then go get it, and when the test date runs out, you have to pay to get it tested.

If you buy a tank from the welding supplier, don't be alarmed when the guy brings out an old beat-up tank. Since you're swapping with rotated stock, you'll always be getting a used tank, but the included valve maintenance and tank testing mean that the tank you get will always be servicable.

If you know safety procedures for high pressure tanks, you can ignore this, but if you're not familiar, keep the protective top on it when you're handling it, and keep it strapped to the wall when it's connected. If one falls over and the valve hits something and gets broken off, the tank turns into a heavy steel rocket, and will go though things like brick walls. I know a welder who saw this happen firsthand, and I'm sure you can find videos on YT.