Are you on a concrete slab? That will make it colder than anything, once the temperature drops and the slab cools down for the winter. Consider adding a subfloor of plywood over foam panels.
Have you stopped all the air infiltration around windows, doors and the base of the walls? Are the wondows double pane, if not that's a source of heat loss. You can place foam panels in them for the winter, especially during the evening when no solar energy from sunshine will enter. Windows have a R value of around 2 where the walsl are R19 with 6" of Fiberglas... a huge difference. They are a large source of heat loss.
Is there a vapor barrier or air infiltration barrier like Visqueen or Tyvek in the walls? This is about heat loss and much as it is about adding heat from an external source. I heat with electricity not because it's cheap but because it's the easiest way I have at the moment.
I wouldn't worry too much about an open flame for dust explosions, not a realistic possibility in a small shop.
I don't like salamanders, too noisey and they burn all the oxygen in the room. A smaller infrared type heater will help, like a Mister Heater.
If you let the temperature drop significantly overnight, you will not catch back up easily in the morning. I keep my shops around 50 degrees when I'm not using them and then heat to 55 to 60 to work in them.
The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)