1) Put 4" (R20) of rigid insulation under the slab with the 6mil poly over top of it and rebar of course 2) Put one wider garage door (insulated) instead of two, you will save money there 3) Don't cheap out on any insulation as it is great for keeping the cold out and heat in during winter and the heat out in the summer 4) Limit the amount of windows to keep expense down 5) run a gas line in for a small unit heater. (won't need much if you insulate really well)
