If you go to a place like Home Depot, you'll find a number of different brands of small electric heaters. None of them will be rated for more than 1,500 watts, because above that the wattage may be too much for the typical home, garage, shed, etc., wiring to handle. You will NOT have to pay $100-200 for one -- it will be a lot less than $100. They're all about the same in efficiency. If you need to, you can always buy and run two of them, but make sure that each is on a different circuit. If your "shanty", as you call it, is not too big and is well insullated, two of the heaters will heat it up. Even one may do the job. I have a well-insullated 28x32' garage and a 1,500 watt electric heater (in addition to a wood stove). When the temp is between 0-40 degrees outside the electric heater will increase the garage temp by about 2 degrees per hour. I don't know how high the heater will get (and maintain) the indoor temp at a given outdoor temp. I've never tried it, though I plan to some day. If its not too cold in the garage, I often turn the electric heater on and aim it right at me when I'm working in a specific part of the garage, rather than firing up the wood stove and heating the whole garage.
