This may not be important to you, but ammo does appear to be a bit costly. I don't have any Weatherby calibers, so take this with a grain of salt. I just see the prices in Cabelas. Perhaps those that use the round a lot have some advice here.
Of course, handloading does go a long way toward solving this problem, but I still think that Weatherby cases will cost substantially more than say, the comparable .338 WM. And if you shoot a lot, the .340 Weatherby may give you a stabbing pain in the wallet.
Cost of components didn't matter to me when I only had two rifles. Now that I have more calibers to load for, I notice it a lot more.
Good luck with your decision!