Value of it is nothing additional to the cost of a base gun except for sentimental value you have for it from being in that unit.
Numerous gun manufacturers offer "commemorative" deals for units coming back from deployments now. The guns are sold a discounted price and the stipulation is typically X# of units sold. They are usually done via email while deployed and it seems all the big handgun companies have a rep that handles this. They'll ship the units to a FFL local once the funds transfer occurs. Once you pass a NICS the commemorative gun is yours.
Sig offers laser ingraved, gold inladed, and silver inladed for thier military commemorative additions.