What about a mobile home? The Dish has the details:
An elaborate 2012 report published by ROC USA and underwritten by HUD found that mobile homes use, on average, far less energy and water than conventional homes or condos (the mobile homes in the study were 940 square feet, larger than those at Pismo Dunes). While models built before 1976, when federal regulations kicked in, sometimes have exorbitant utility bills, newer models made to Energy-Star efficiency standards can reduce the combined costs of electricity, gas, and water to well below $1,000 a year, even in the hottest and coldest parts of the country.
And they look a lot nicer than your grandma’s mobile home.