Thank you all for your replies. The problem with finding the cost per kilowatt hour for the space heater is that I still have no basis for comparison. My electric bill would show the kilowatt usage only for the entire month, and would include usage for lights, appliances, etc. as well as heat. And even for heat alone, it would be over a long period of time.
I guess my question should be: for a given hour of usage, which is cheaper: to crank up the apartment heat by one degree, or to turn on the space heater to medium? Even then, it would be hard to figure, as probably the cost of cranking up the apartment heat would depend on how cold it is outside, while the cost of using the space heater would remain constant.
As for wearing warm socks, etc., granted, but I still think that most people use some amount of energy-produced warmth in their homes; we are not living in icy igloos and wearing warm socks. The house does not have to be heated to greenhouse levels, but come on, guys!