American Council for an Energy-Efficient Economy (ACEEE), Report Number U1402, March 2014, by Maggie Molina. (Free registration required to access full report.)
http://www.aceee.org/sites/default/files/publications/researchreports/u1402.pdf

"As efficiency programs gain wider traction as a utility resource, the need increases in step for high-quality, comprehensive and consistent data metrics on energy efficiency program costs and cost-effectiveness. In this report we review utility-sector energy efficiency program costs in recent years (2009-2012).  We collected data from reports by program administrators to calculate the levelized cost of saved energy (CSE), which is the best way to compare energy efficiency to other energy resource options."