「誰がそんな高い服買うの!」は下のように言えます。
1) Who would buy such expensive clothes!
2) Who would buy clothes that cost that much money!
Who would 〜? の用法で「誰が〜するのものか」という言い方です。
Who would buy such expensive clothes. で、「そんな高い服を買う人がいるはずがない・誰もそんな高い服を買うわけがない」と言うニュアンスです。
ご参考になれば幸いです!
ご質問ありがとうございます。
・「Who would buy such expensive clothes?」
(意味)誰がこんな高い服買うのよ!
<例文>Who would buy such expensive clothes? It's so expensive I'd be scared to wear it.
<訳>誰がこんな高い服買うのよ!高すぎて着るのが怖いよ。
ご参考になれば幸いです。