I have for sale a gas furnace, $150
down draft or downflow,
working condition,
70,000 BTUs input 57K output,
Brand NORDYNE model MGHB-070 abfc-06
can be used on home or garage or shop heater,
you can even install it on top of the area you want to heat as depicted on the last picture.
I also have a NEW, never used AC 3.5 TON A-frame evaporator unit, $200
that can be used in this furnace,
or it can be used by itself,
Brand NORDYNE model C3BA-042C-b
20" x 24" footprint 76" height with space under for the AC A-frame, it can also be mounted on top of base or duct