I use a few different ways to keep my cost down which I'm not sure you'd want to do (and some are situational)

1) I don't run the heat until I absolutely cannot stand it. If I am cold in a sweatshirt in the main part of the apartment, I turn it on (although not very high)

2) In my bedroom, I run a small space heater to keep me warm. It's set to run at 78F (and will set off if it detects the warm getting warmer than that)

3) I live in a third floor apartment, so I have the heating from the apartments below me filtering up.

4) Our only open walls are the wall of the living room where the front door is, and the south-west facing wall.

Some other little things I do are put throw-rug type blankets over the windows of my room and the living room, keep the porch locked tight so the air doesn't come in and keep my bedroom door shut.

Even though it works well, I try to avoid running the oven very long. It does warm the kitchen and dining area up nicely, but the oven costs more than my heating (we only have electric, no gas)

So, I guess that doesn't really give you an idea what it'll cost you, but maybe it'll give you some cheap easy ideas on how to keep your costs down once you have them