How much running an electric space heater for 24 hours would would cost would depend on how much your electric cost is per kwh.
But I'll go by my own kwh cost to provide a close answer.
I pay 16 cents per kwh including all the other fees.
So a 1500 watt space heater will consume 500 watts over the 1,000 kwh so lets say 20 cents per kwh to run the space heater. I'm not great at math so forgive me if I'm wrong."
So let's say at my cost it will cost 20 cents per hour to run a 1500 watt space heater. If you times that 20 cents per hour x 24 hours you'd come out with a cost of $4.80 per 24 hours of run use.
So if you run the space heater for 24 hours a day it would cost you $4.80 per day x 30 days would be $144.00 per month.
Most people don't run the space heaters 24 hours per day though unless they're trying to use them solely as there heat source.
It's cheaper to just run a furnace as you'll need more than one space heater to heat your whole house so your cost could go up to $19.00 per day and your electric bill would be almost $600.00 per month for barely staying warm.
Space heaters are good for taking the chill out but I wouldn't try to use them for your sole heating source as they're very costly to keep running.
You could almost pay for a new furnace with one months heating bill from the space heaters use if you're using them as your main heat source with nothing else.
It'd be cheaper to heat with natural gas or propane. Or even install a wood stove and heat with that instead.