Home Depot only has 10 and 20lb bottles, so if you have 5lb you're out of luck. But they are the cheapest place I've found. Not all the stores have them though. They all have Propane in the cabinets out in front of the store, if they also have additional cabinets of other gases, then they carry it. The Park and Tollway Home Depot has it. I don't know the others offhand, but at least 2 others in Plano have it I think. But the ones in Dallas I don't think have it at all. As others have said, any welding shop will do it. They will also usually let you trade the tank plus some cash to upgrade to a 10lb tank and then you can go to Home Depot.