I had a similar issue as far as a rental/ low use fee on a underground tank. When i put my tank in it was a lease with a one time lease fee of about $200. after a few years when we got our price lock contract for gas we sent it in and shortly after we got a statement for a rental. I called and they said that was built in to price lock contract. When u sign for price lock u are also agreeing to a rental fee. I called and they said you can buy your tank? They gave me a price of $600 so i bought it. Now no 50-75 a tr rental and i get gas for .25-.50 / gal cheaper. Gas supplier said the extra price is built in for the maintance of you gas system. The "free" service calls i guess like if your regulator goes bad or something. My payback should be 4 yrs or so. I shopped and got propane for $1.69/ gal