This article reviews seven cost-benefit analyses of substance abuse prevention programs.  The programs were all effective and cost-beneficial and reported savings per dollar ranging from $2 to $19.64. The authors note that the large range is attributable to variations in outcomes considered, cost calculations, and general methodologies. 

Swisher, J.D., Scherer, J., and Yin, R. K. (2004). Cost-benefit estimates in prevention research. Journal of Primary Prevention, 25(2): 137-148. DOI: 10.1023/B:JOPP.0000042386.32377.c0 http://www.springerlink.com/content/r0tvq0740p228018/ 

Authors: John D. Swisher, Jennifer Scherer, Robert K. Yin