Thinking about buying a 20 cubic foot cylinder from Praxair. 2' tall, $100 to 'buy' the tank and $25 a fill after that. #1. Good deal or bad deal? #2. How long is a tank of that size liable to last. I'm not a serious metal fabricator, but I am gonna try and weld 90% of buggy cab next weekend. How often can I expect to refill a cylinder of that size when it's used occasionally?