Does not have to cost a lot. When a friend of mine updated his camp with an actual cabin, I bought his old trailer for $300. (he had to replace some tires; included in price). I've had it for about ten years now. Pretty sure I got all my money out of it.
Nothing to look at, It was broken into once, so I don't keep anything of value in it now.
But it keeps us dry and warm... well when it gets below zero, it is a full time job keeping the wood stove going.

Now, three generations having fun at the old shack.
