I can't imagine that one couldn't build a shipping-container sized building with wood for a lot less than $2000. Fir 2x4 and 2x6 timbers are literally dirt cheap right now. Throw in some siding, drywall, some insulation, and some roofing materials and you'd have a pretty nice shell of a house for about the same price. Best part about using wood is that you wouldn't be stuck with the long, skinny configuration; you could alter the dimensions quite a bit without too much extra cost.