Well, as someone who has spent way too much time in theater, the first question I would ask is, do these guys already have a good fixed blade. If not, I would go for a capable fixed blade first and foremost. A fixed blade is an immensely important piece of equipment that will be used constantly. The folder is a backup that will certainly be used for random menial tasks, but I have found that a mid length, comfortably sized and ergonomically shaped fixed blade is an absolutely necessary tool, whereas a folder is not. A lot of guys will also tend to go for the most wicked looking blade they can find and then end up regretting it later. The fact is, if you're going for your folder in a combat situation, you're in deep shit. Having a fixed blade that could serve as a tool and a weapon is logical. Your folder should be an effective tool first, and a weapon running a far distant second.
Now, if they do have a fixed blade, then you can move on to a folder. Generally, I would say that MOST, but certainly not all, of the guys in my crew preferred to have folders that ran around 4", with a nice sharp point, steel that is easily and quickly sharpened, good strong lock, easy and quick to open. While alot of the so-called "tactical" folders have those huge thick and wide drop point blades, I, and my teammates, never really found them to be a viable choice. Yes, I have seen guys carrying those big double recurve beasts that are 2" wide at the belly of the blade, but a knife with a slimmer blade ends up being a lot more useful for a variety of tasks, and that is the most important thing. When you are overseas, you can't just run to the store and get a new tool, so everything you carry needs to be able to effectively perform the greatest number of tasks possible.
You see a lot of Benchmade 710's which is, in my opinion, the idea military carry folder, but its likely a little outside your price range ( about $125 ). I know a few guys now who carry CRKT Firesparks , which is a 3.9" and effectively shaped blade and is also quite affordable( about $42 ). Even the G10 S30V Kershaw Leek only runs about $70 on ebay and is a great little knife to perform the kinds of tasks necessary while in the field. You also can't go wrong with a Spyderco. There is a reason that the Endura ( $65 ) and others have been popular with the military for years........because they are great knives that have served Military members well.
Best of luck in your search and my prayers are with your family members.
WH