The metal siding on the shop and house could be killing your signal.  Outside antennas would probably help. Or at least set the router in a window.

Have never used or heard of Ayrstone.com, but they provide networking products for a farm environment. I just read an article about them in a farm magazine.  You  might get by with one outdoor hub at a cost of $250.  There are cheaper alternatives but they can be complicated.  If you have trouble following  Bwire's direction you might be better off with something like this.