I am looking into building a 600 sq. ft. house with the west and north sides being earthbag walls buried to at least 6 feet into the side of a hill hoping to get the earths thermal mass heating and cooling. No sun ever on 2 walls. That has gotta make the place cooler. Except for extensive labor you can't bet the price. Plan on having at least two large water tanks mostly buried with my battery power supply box between the tanks hopefully keeping things cool.
This will give me my nice view of the Chisos out the east side which will be a large covered patio. Check out pictures of my existing place and views from my place at http://www.airqualityindoors.com/jpstplace.htm.