The cost-effectiveness of delivery methods for an eating disorder prevention program is reported. In an effectiveness trial (enrollment 2013-2015) comparing three formats (clinician-led, peer-led, and Internet-delivered) for delivering the Body Project eating disorder prevention program to college women versus an educational video control, the peer-led method was more effective than the three alternatives at preventing onset of eating disorders over 4-year follow-up. Eating disorder incidence was 19.3% for clinician-led groups, 8.1% for peer-led groups, 15.5% for Internet-based eBody Project participants, and 17.6% for educational video controls. Delivery costs per person are reported for the Body Project, including participant time, and the cost-effectiveness is calculated for peer-led groups versus the video control. Data analyses were conducted in 2019-2021. Delivery costs per person for the Body Project, including participant time, were approximately $96 for clinician-led groups, $80 for peer-led groups, and $22 for the eBody Project, compared with $9 for the educational video control. For each additional case of eating disorder onset that was prevented by the peer-led groups, compared with the video control, the cost was about $740. There were no differences in health care utilization across condition. Eating disorder prevention costs via the Body Project compare very favorably with the costs for treating an eating disorder, which previously have been estimated to range from approximately $20,300 for cognitive-behavioral therapy for bulimia nervosa to approximately $119,200 for adequate care treatment of anorexia nervosa. These analyses demonstrate the economic value of the Body Project for preventing eating disorders among college-age women when delivered in peer-facilitated groups. ClinicalTrials.gov Identifier: NCT01949649.