If you want to go fast, you have to pay for it. If you were to spend $50 grand on a Corvette, you wouldn't fill it up with cheap low octane gas from a noname gas station to save a few bucks would you?
Same thing with Weatherby, its a premium rifle and they have their own premium loads for it. You sure wouldn't want to shoot substandard or low quality ammo through a rifle that costs several times as much as an ordinary rifle if you bought it for performance. The company has cornered the market for their premium ammo, they can pretty much charge whatever they want as they are the only kid on the block.

Alcohol, Tobacco, and Firearms... who's bringing the chips?