Actually, it is well on the high side. The best rated 50 BMG brass (RWS) is available, and in stock, at $4.35 each - TenX Bullets: RWS components and ammunition
Unless you are an FCSA (Fifty Caliber Shooters Association) member, you probably don't know about them. Currently, as best I know, they are the only supplier in the US.
The majority of 50 BMG shooters buy brass that's once fired, USGI surplus, at 60 cents each, or less (see Pat's Reloading - Prices
). Only match shooters ever concern themselves with new, match brass offerings. Thankfully, at least the good stuff is available for those who are willing to pay the tab.