purse strings
Idiomatic expression referring to control over spending or financial resources, often used in phrases like 財布の紐を握る (hold the purse strings) or 財布の紐が固い (tight-fisted).
My wife holds the purse strings when it comes to household finances.
He's tight-fisted, so he rarely parts with his money.
金銭感覚 refers to one's sense of money or financial prudence, whereas 財布の紐 specifically evokes the image of tightening or loosening purse strings.
Literally 'the string of a wallet/purse', from the image of a drawstring pouch used to hold money. The idiom naturally extends to control over spending.