Thats a good deal on the small tank LP. I don't know about the current tanks, but aren't they sized at 20 lbs, but have less capacity ?
20lb = 5 gallon ?
30lb = 7 gallon ? ) forklift LP tank
I think the price for the 20lb filled at the local agway was $18, I recall the 30lb at $26, my ford tractor runs off the 30lb tank. The latter price I believe correct, headed over there to get one filled shortly, will double check but that puts it about $3.71 if the gallon capacity is right as shown above. It was higher, but I forget, I recall in '04 the price was 1/2 that, was less than gasoline significantly, I get about 4-5 hours run time at medium throttle, all depends on what you are doing.
The thing was when it was higher, I really started to believe it was a rip-off, but they are closer than anyone else, very nice people, service and so on, but I think it did drop at some point, was like $5/gallon and one thing is for sure, you bring in a tank partially filled, as I do on occasion, so not to be hassled by running out, I have only 2 tanks, they do not charge by the gallon, only by the tank size. Given I don't run this tractor a lot, I'm ok with it, glad they dropped the price a little, but if I was running more hours, more fuel, I'd have to find another source. There's always a teenage kid filling them for the most part and you have to watch the gallons, or the vent on the 30lb til it shows a nice stream of mist, so as not to be shortchanged. Its one of those things that you are aware of, but not worth raising heck over, rather support the local business's, if I used more, I'd speak with them first about it, a nurse tank and the means to fill smaller ones would be great and cost savings if you used any real volume, in the long run, but I just do not use enough. If they did sell by the gallon, maybe its a hassle, being a retailer, hard to say.
TSC is across the road from me, not sure if they do the tank exchange, I don't as I have quick connectors on mine for my grill, need a special tip to refill, so I just take them to agway, sucks when the kid loses the tip or leaves it on someone elses tank LOL and you can't get filled, though after thinking about it, those quick connects should come off I suppose and allow the other nozzle to work.