It really depends on how well you like the building, how easy it is to dismantle, and how well it is built.
Here's my attempt:
http://wood.bigelowsite.com/shed_moving/index.htm
There were two sheds. The first was only moved half a mile, and the second (mine) maybe 10 miles, and all back roads.
Initially, I was going to pull the roof off, and then the sides, but after spending 5-6 hours over two days trying to partially dismantle the building, I gave up and just hauled it as-is.
A solidly built 8x12 building has at least $800-$1,000 worth of materials into it at Home Depot prices. A cheaply built one has maybe $300 worth of materials. Either one can be built in a couple of days.
It's going to cost you at least $150 to move either one (federal mileage rate). What's your time worth?
Myself, I'd think long and hard about moving a small building that far. I had the opportunity to move the one in the above pictures again when I moved to my current house, and decided against it. Wasn't worth the time and effort, and that was a nice, solid shed, and I was only going 30 miles.
-Steve