Karl,
Do your hardware/lumber yards/landscape supply retailers not have propane to refill a 20# tank?
There are several here in NH within a 10 mile drive that sell a refill for between $14-16.
Your tank has to be replaced once every 10 years. I have two tanks, so I never run out in the middle of a BBQ with people over.
The big box hardware stores all sell refill tanks. One hardware store nearby refills tanks, but it seemed like half the time they didn't have a propane guy available.
I finally just ended up driving to a depot site that sits on the pipeline and whose main business is trucking it to people who have big tanks for heating. They are also the only ones I found to charge by pound for a partial fill rather than a flat rate based on tank size.