How much money do you think I should put in the envelope?
How much is the going rate for congratulatory wedding gift money these days?
この場合、次のような言い方ができますよ。
ーHow much money do you think I should put in the envelope?
「ご祝儀袋にいくら包んだらいいと思う?」
ーHow much is the going rate for congratulatory wedding gift money these days?
「最近の結婚式のご祝儀っていくら?」
congratulatory wedding gift money「結婚式のご祝儀」
ご参考まで!