You don't know how much it means to me.

I wonder how much it costs to fly to London.
ロンドンまで飛行機で行くといくらかかるんだろう。

Sydney? I wonder how much that's going to cost.
シドニー？！いくらするんだろう… 

You can decide how much you're going to pay on your credit card.
どれだけの額をクレジットカードで支払うかを決めることができます。

You don't know how much it means to me.
私にとってそれがどんなに意味深いことか、あなたには分からないでしょう。

There are no words to describe how much he means to me.
彼が私にとってどれほど大切な存在か言葉では言い表せません。