He gets a little carried away when it comes to spending money.
この場合、次のような言い方ができますよ。
ーHe's extravagant in his use of money.
「彼は金遣いが荒い」
to be extravagant in one's use of money で「金遣いが荒い」
ーHe gets a little carried away when it comes to spending money.
「彼は金遣いがちょっと荒い」
to get carried away when it comes to spending money で「金遣いが荒い」とも言えます。
ご参考まで!