make a mint
To earn a very large amount of money, especially by doing something very successfully. We'll make a mint if we can manage to secure a trading partner in China. I hear Sarah is making a mint with sales from her latest novel.
make, etc. a ˈmint (of money)
(informal) make a lot of money: They’ve made a mint of money with their new range of travel books.You can earn a mint selling ice cream on the beach in July and August. OPPOSITE: take a bathA mint is a place where money is made.