How much do you have? The cost all depends on your imagination, size, and materials used. Our shack is 6x8, but is really overbuilt, so it is quite heavy. However, on a -20 day and the wind howling it stays nice and warm with the woodstove going. Build what you can afford, and keep in mind the weight, we use 4 wheelers to pull ours. Good luck with your future build.
Johnnyrotten