Military photographers are not allowed to cover an event like this for the purpose of shooting couples. So a military photographer, for free, won't be there.
I've done a lot of these types of shoots in the past for each of the services. You're right about the time spent on something like this.
Suggestion: Go through a copy of Rangefinder or Shutterbug and see what labs are charging for these kinds of packages.
Next: KEEP IT SIMPLE! If you don't you find yourself taking a dozen photos of each couple or you'll lose customers while Johnny and Susie are trying to make up their mind as to what package to order.
The most common package is 2-5x7, 4-w/s and sells, as a general ule, for $10-$25.
Keep the price simple as well. $10, $20 is easier to collect than $25. You don't want to be making change all night or lose a customer because you can't make change. Chances are you won't be in a place that'll have a cashier readily or willingly available.
Are you going to shoot film or digital?
If you shoot digital than I have another suggestion. How about a package that is 1-5x7 or 1-8x10 with a CD that has an emailable photo and another hi-res for the 5x7 or 8x10.
Chances are you will not get a lot of reprint orders. So if you shoot digital or 35mm and offer the 5x7 and the CD you just might get a lot of customers. Much better to have 100 customers at $20 and no further obligation than to get 50 customers at $25 and have to keep all the negs, etc. available for a dozen or less reprints. Not to mention 100 satisfied customers gives a LOT of word of mouth advertising.
And seeing that a lot of bases are now joint service you might be looking forward to the Army Ball, Navy Ball, Marine Corps Ball, and even dining in and dining out, and the Firefighters' Ball.