I have a 26x40 shop that I heat with a propane 70,000 btu furnace.
It's made by Modine and it's called a Hot Dawg. It hangs on the
ceiling and vents out the wall. I bought it on the internet through
QC Supply for around $600 delivered. I did bring in a 320 lb propane
tank that's only used for this furnace, then it's easier to gauge how
much I'm using. Last winter (in northern WI) I used about $300 worth
of propane. When I'm not using the shop I keep it set around 45 and
it takes only a few minutes to heat up to 65.