The Marine Corps Tartan is NOT made by numerous mills like so many other tartans are. It's much like the Irish National Tartan in that, it's poopular, it's beautiful, and it's protected by the fact that the mill that produces it can charge whatever they want.

Those companies that HAVE the tartan (and are willing to make it into a kilt) are actually taking the gamble that they can sell it. They're putting-up the funds to acquire the tartan, and are spending more on it than other tartans.

If your heart's set on the Marine Corps Tartan, you'll need to work some more overtime and be patient. Sometimes, those things are the most charished.