It's cheaper to buy ... at a store than it is to buy ... at Amazon.
Buying ... at a store is cheaper than buying ... on Amazon.
ーIt's cheaper to buy those at a store than it is to buy them at Amazon.
「それらをアマゾンで買うより、店で買った方が安い。」
It's cheaper to buy ... at a store than it is to buy ... at Amazon. を使って「～で買うよりも～で買うほうが安い」と言えます。
ーBuying those at a store is cheaper than buying them on Amazon.
「それらを店で買うのは、アマゾンで買うより安い。」
Buying ... at a store is cheaper than buying ... on Amazon. を使って「～で買うよりも～で買うほうが安い」とも言えます。
ご参考まで！
"It's cheaper to buy it at the store than on Amazon."
「アマゾンで買うよりも、お店で買ったほうが安い」
"cheaper" は「より安い」という意味で使われます。"to buy it" は「それを買う」という意味で、"at the store"（お店で）と"on Amazon"（アマゾンで）という2つの場所を比較しています。
他の表現:
- "It’s less expensive to buy it at the store than on Amazon."
- "Buying it at the store is cheaper than on Amazon."
カナダ 
アメリカ合衆国 
