If something is ‘a drop in the ocean’, it is a small amount.
A person who is a ‘night owl’ usually stays up late
.
If you do something ‘now and then’, you do it occasionally.
'A month of Sundays' means a long time .
If you say you are 'off-colour', you feel ill
.
If you are envious of someone, you are 'green with envy
'.
If you get extremely angry, you 'hit the roof '.
It doesn’t cost much money. In fact, it’s 'dirt cheap '.