The 11 pounders,2.6 gal, are $56.97 through Home Depot with store delivery. I went down from a 20 lb tank to the 11 to save tongue weight
since we use it primarily to run the refrigerator
so don't use that much; 1.7 lb on our last 20 day outing.
When you think about it, the collar, base and valve are all the same. The difference is in the material for the tank and somewhat more welding. The reason for the price differential is primarily that the demand is so much higher for the 20 pounders, and therefore more competition for that market, which keeps the price down.
When is a deal not a deal? When you buy something you really don't need because it is cheaper.
As far as swapping tanks, you may recall a thread not long ago about the 'full' swap tanks only have 15 or 16 lbs in them. Where is the deal there?
Next time you swap tanks, weigh the tank when you get home. Deduct the tare weight, the number behind 'TW' on the collar, and you will see what you actually bought. You may have only bought 4 lb more than my 11 lb tank. Convenience is generally not cheap.
I now use my 20 lb tank to boil crawfish and render beeswax.