싼 게 비지떡이다: Cheap and inferior. Penny-wise and pound-foolish.

싸다: cheap, low in price

비지떡: a fried pancake made of tofu residues and rice flour/flour

비지: tofu residues

→ 비지 has been considered as a very cheap, petty food for a long time. When we say 싼 게 비지떡이다, it means ‘you get what you paid for,’ ‘you never get anything good for a cheap price,’ ‘cheap and inferior.’