He overextended himself financially when he bought that coat, but it looks really nice on him.
He spent more money than he should have on that coat, but it really suits him.
ーHe overextended himself financially when he bought that coat, but it looks really nice on him.
「彼は経済的に無理をしてあのコートを買ったが、とても似合っている。」
この場合は、 overextend himself financially のように言うと良いでしょう。
ーHe spent more money than he should have on that coat, but it really suits him.
「彼は無理をしてあのコートを買ったが、とても似合っている。」
spend more money than he should have on that coat 「あのコートに使うべき以上のお金を使った」と言った方が自然だと思います。
ご参考まで！
カナダ 
