One thing to remember, electric heat is always basically 100% efficient. There are some heaters out there saying they are more efficient than other electric heaters, that's not true. A $20 electric ceramic heater at walmart will be as efficient as the $400 ones that are supposed to be a break through.
The money savings that they talk about with these space heaters is that you can place them in the rooms you spend a lot of time in and turn the furnace down a few degrees for the rest of the house.
Here is a nice fuel cost calculator:
http://www.woodpelletinfo.com/calculator/
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