FYI, the Gates family has donated to Duke (and Harvard, as well as probably other leading universities) with tremendous generosity. For example, the French Family Science Center (http://www.architect.duke.edu/projects/completed/French.html), which is named to honor Melinda French Gate’s (Duke '86, Fuqua '87) family, is a major, capstone facility opened on Duke’s West Campus several years ago. Of course, this philanthropy is in addition to the Gate’s Family Foundation’s unprecedented global support for various initiative, especially health care.
To respond to the initial question, I really don’t believe a price could be accurately calculated; there simply are too many variables. However, I suggest the “brick and mortar” investment – although huge – would be inconsequential when compared to the costs of attracting first-class intellectual capital to any new university. Top faculty and administrators require competitive compensation and will not leave their existing jobs without facilities, research assurances, staffing, and so forth that meet their requirements. @whenhen’s points are spot-on.