Dear Valkman:
There's already "reasonable" priced Brazilian MagTech .500 S&W Magnum 400 grs. SJSP ammunition on the market already. This ammunition is also properly C.I.P.-approved. I don't know about the prices in the U.S. but in Germany a 20-rd. box is more like EURO 19,70 retail (= circa US-$ 23.00 to 24.00). Of course, that's still far from inexpensive, but affordable.
I assume that most guys owning a .500 S&W are purchasing a couple of boxes of factory ammo in order to get a "feeling for the thing" and to have some empty brass cases available for handloading, right?
Regards!