A friend of mine owns the same unit, and uses it in the same manner.
He is conservative and doesn't find the extra bill from cranking up
noticeable..

Around here a therm is about $.90 and 45,000 would use one therm every
2 hours. If the heater ran full tilt for two hours you couldn't stand
to be in the shop.

He keeps his set for just above freezing, but keeping it in the upper
40's for woodworking tools to not condense I think would be wiser. If
the heater is not ALL or nothing, you could dial it down to 5K btu's or
something and that might be more managable as an ongoing heat level.
Alan