What size of space are we talking about, for you might be just as well doing what I do and using a cheap 2kW fan heater with thermostat to keep your space at a constant temperature, and it can be used as "fan only" to help circulation in warmer summer months.
The other advantage is the warm air is forced around the room/tent before going up into your extract, whereas with tubular or any other pure convection heater a hell of a lot of the heat is wasted as it goes straight up and into your extraction, kinda defeating the purpose of the heater.
Costs are negligible, in reality, as the heater will not be running nearly as much as it would had it been a pure convection or radiating heater. I know what my electricity use is, and the extra efficiency of forced heating over convection/radiation is a major game changer to me.
Just don't point it at your pots or you'll cook the roots.