One of the best resources is this study by Kaiser Permanente that analyzed the costs associated with not breastfeeding, in order to determine the benefits of sponsoring a lactation program for employees.
http://www.visi.com/~artmama/kaiser.htm The conclusion is that “Infants who were breastfed for a minimum of 6 months experienced $1,435.00 less health care claims than formula fed infants.”
It’s old (1994-1995) but health care costs certainly haven’t gone down any since then.

A few more scientific studies:
“Health Care Costs of Formula-Feeding in the First Year of Life”
http://pediatrics.aappublications.or...l/103/4/S1/870
“The Economic Benefits of Breastfeeding: A Review and Analysis”
http://www.ers.usda.gov/publications...13/fanrr13.pdf
Cohen, R. et al. Comparison of maternal absenteeism and infant illness rates among breastfeeding and
formula-feeding women in two corporations. Am J Health Promo 1995; 10(2):148-53.
http://www.breastfeedingworks.org/comparison.pdf
Cohen, R. and Mrtek, M. The impact of two corporate lactation programs on the incidence and duration of breastfeeding by employed mothers. Am J Health Promo 1994; 8(6):436-41.
http://www.ncbi.nlm.nih.gov/pubmed/10147273
Major, DA et al. Child Health: A Legitimate Business Concern. Journal of Occupational Health Psychology. 2004 Oct Vol 9(4) 306-321.
http://psycnet.apa.org/index.cfm?fa=...2004-19696-004
Slusser WM et al. Breastmilk expression in the workplace: A look at frequency and time. Journal of Human Lactation, Vol. 20, No. 2, 164-169 (2004).
http://jhl.sagepub.com/cgi/content/abstract/20/2/164
Click, ER. Developing a Worksite Lactation Program. MCN, American Journal of Maternal Child Nursing. 31(5):313-317, September/October 2006.
http://www.mcnjournal.com/pt/re/mcn/...195628!8091!-1
Is There Competition between Breast-Feeding and Maternal Employment? Brian Roe, Leslie A. Whittington, Sara Beck Fein and Mario F. Teisl Demography, Vol. 36, No. 2 (May, 1999), pp. 157-171.
http://www.jstor.org/pss/2648105
And some additional resources:
Bibliography on “Economics of Not Breastfeeding”
http://www.naba-breastfeeding.org/images/Economics.pdf
“Breastfeeding Friendly Workplace Policies” (PDF of a booklet)
http://www.breastfeedingtaskforla.or...rief_FINAL.pdf
“For Business -- Breastfeeding: The Best Investment… Worksite Support of Breastfeeding Employees Improves Your Bottom Line”
http://ww2.cdph.ca.gov/programs/Brea...Investment.pdf
Lactation Support Program toolkit from the CDC
http://www.cdc.gov/nccdphp/dnpa/hwi/...tion/index.htm
Breastfeeding Support at the Workplace: Best Practices to Promote Health and Productivity (includes examples of “model programs”
http://www.businessgrouphealth.org/p...ding_brief.pdf
Breastfeeding Resources for Employers from the California Department of Health
http://ww2.cdph.ca.gov/programs/wicw...Resources.aspx