You can actually reload the .300WbyMag for less than what it costs to load similar loads in a .308 or .30/06.
Widners, PatsReloading, and GI-brass sell pull down mil-surp powders from .50bmg ammo.
I've got a .300RemUltMag that I load with either PrviPartisan or Remington Cor-lokt bullets from before the big price increases of several years ago. I bought 500 180gr Corlokts for ~40.00.
I can load my big .300 for less than the cost of my .30/30 or .30/06 as I bought powder for $50 for 16lbs (WC-860 from Wideners). Heck I even bought a .257WbyMag because it wouldn't sell because of the cost of ammo.
I'm getting 3,300fps from a 180gr bullet from the .300RUM with 107.0gr of WC-860 (used H870 data as starting point), and 3,550 from .257wby with 80.0gr of WC-860 under a 100gr PtSpt (Hornady blems from MidwayUSA for $8.00/100).
I've got less than $500 in both my .257wbyMag and .300RemUltMag.
I'd definitely get the .300wby and enjoy it. But, You'll definitely need to reload for it to get best benifit from it.
You can also load with Acc.Arms #5744 and get .308wcf performance from the big Weatherby.