It would be cheaper for us to buy directly from B, rather than through A.
We could save money if we order directly from B, and not go through A for it.
ご質問ありがとうございます。
① "It would be cheaper for us to buy directly from B,"=「Bから直接買う方が私たちにとって安くなる」
"rather than through A."=「Aを通すよりも。」
② "We could save money if we order directly from B,"=「Bから直接注文したら私たちはお金を節約できる」
"and not go through A for it."=「Aをそのために介さないで。」
ご参考までに。