It depends entirely on how they normally structure the purchase situation.
I assume you'll be taking formals of the couples, as well as PJ of the event ?
Unless they have a set procedure (and they are military after all) I'd treat it like I do a Prom. I'd charge command a fee for shooting the event ( $500 or whatever you think the traffic will bear ) and then present the formals on line with a purchase option (exposure manager does a great job).
Here's an example
http://tomthompson.exposuremanager.com/ Prom password is colonial.