The Denver Alumnae chapter of Alpha Phi holds a similar event and they seem to have great success with it.
Press release from 2004 -
The Denver alumnae chapter of Alpha Phi and Cherry Creek High School's About Hope4All, a student organization dedicated to community service benefiting children, hosted the 6th Annual Prom Dress Exchange on March 20, 2004 at the Marriott Denver Southeast. Young women were invited to attend to find the "perfect" prom dress for prom in exchange for a $10 donation.
"This event allows young ladies the chance to experience high school prom without the financial burden. Anyone interested in being involved can donate a dress for an individual that cannot afford to buy a new one," said Holly Brown, Alpha Phi Denver alumnae chapter marketing director. Women who selected dresses last year were also given the opportunity to bring them to the event in exchange for a new dress.
Mrs. America 1991 and Pageantry Magazine columnist Kristianna Nichols also offered hairstyling tips to attendees.
And their press release for their upcoming 2005 event is on their website:
http://www.denverphis.org/alphaphiandthecommunity.htm