I bought a 70lb tank at a yard sale but can't get it refilled. Seems you need to have an account at the refill place and rent their tanks for $100/yr then it's around $125 for refills. I doubt I'd need more than a tank a year for the size of my little grows and would only run at around 800ppm. With a sealed room it wouldn't take much to keep it at 800. I can keep it well over 800 just with my little alcohol lamp and it only uses around 50ml/day of methyl hydrate. I have a CO2 controller but have only been using it to see how the levels go up with the lamp and even just a candle. Both get over 1500 in 20 min or so. Working on the plants for half an hour with the door closed gets over 1000ppm in 15 min.
I have easy access to a gas line down there but then would need a burner and tho I'm sure I can hook it all up safely if there was a fire anywhere in the house and they found my DIY hookup my insurance would cut me off for sure. Not hiring a gas fitter to do any work down there either. Too paranoid for that.