If you buy a tank, get a copy of the test documents, or no deal. The fuel supplier may want it if they didn't provide (sell) you the tank. You may find they will at least negotiate a reduced price on the tank if you buy it from them. I am surprised you use so little. Most of my homeowners that are on propane use MUCH more.
Do they heat with propane?
Have families?
2 of us, instant hot water (on demand, much less usage than a standard tank) and a gas cook-top. That's it.
I asked about purchasing a tank from my current company and they wanted $800 for the 250g tank.. I told them no thanks!
I may be able to convince them to get me a 2nd tank as I could use one for my 'in-laws quarters' we plan to make above the garage and one for the house. (This is all in the way future right now)
Thanks for the advice about the documents.