cost an arm and a leg
I saw a beautiful coat but it cost an arm and a leg.
我看中一个很漂亮的大衣，但是太贵了！

Tighten my belt
To cut down on spending because there is less income than before
由于收入减少，所以开支也相应减少。

in the balance
The outcome of football match is hang in the balance.
足球比赛的结果还悬而未决。

in the bag
The election is in the bag unless the voters find out about my past.
如果我的黑历史没被投票的人发现，那选举这事儿，就是稳操胜卷了。

Keep us cool
He kept his cool even though it was clear that he was being unfairly treated.
即使受到不公平的待遇，他还是保持自己清醒的头脑，保持淡定的心态。