Where can I get propane tanks and refills cheaply?

We have a couple drums of waste oil collected, but the efficient waste oil heaters cost thousands of dollars and I’m not looking to heat the whole shop. If I was, that would make a lot of sense in the long run.

I just want to heat the “office” area which has been sectioned off.

The polar bear roamed the tundra in the shop area last year with the occcasional aid of some high powered lights that throw a lot of heat. Most of the time he didn’t even wear a jacket LOL.