Finding, buying storing 40lb and smaller tanks is expensive. I check Craigslist and occasionally go to yard sales always looking for propane cylinders. Haven't found any that didn't cost nearly as much as just buying a blue rino tank with out an exchange. To get a 40lb tank bought and filled is probably around $130 and that's with me pulling a high vacuum to dodge the first time purge fee. $130 for 40lb of fuel, equal to about 800k BTU is pretty horrible dollar to energy conversion. If you just want it for cooking get a white gas stove and burn gasoline in it, save hundreds of dollars. Now to get to the bulk propane part of the post. There is some one near me selling a 250, 300 and 500 gallon tanks for cheap, but they look like they are at least 20 years old. Only problem is I don't know if I can get it filled. I think I can but not absolutely sure. I know with the small ones if they are lacking the overfill protection device (the old style, that's only used on 100lb and up now) or are over a certain number of years old propane refill stations won't refill them. Are bulk tanks in the size classes I mentioned the same way? Is there something besides bullet holes, or damaged valve stem to look for on a big tank that would make it unfillable?