Why are semi-auto belt-fed machine gun replicas so expensive?

I have been looking at some semi-auto machine guns, such as a semi auto Browning M1919, M60, M240, MG-42, etc. And they're all ridiculously expensive. They're so expensive it would be cheaper to buy a water-cooled transferrable machine gun. Does anyone know if there's a reason why they are so expensive? Is there a copyright where they need to pay the original company a certain amount of money to sell a semi-auto replica? Are belt-fed designs just that expensive and complicated?