"The Army has invested about $12 million into the project, which includes the cost of renting the 14,500-square-foot facility for two years and creating content for the site..."
I suppose it will all come down to how effective it is in getting the message across and how it's recruitment rate compares with other methods. I'm actually rather surprised that they hadn't done something like this earlier.
I would imagine also that the quoted dollar figures reflect the entire cost of development of the project, and so if they decide to expand into other malls the cost will be dramatically less for subsequent outlets.