It means you bought or traded something and unintentionally received more product(s) than what you paid or traded for. That additional product(s) was therefore “Free” however there was a transaction of money, goods, or services required to receive the free item therefore it was “on the cheap.”
Yo man I bought a 6 pack a socks and there was 7 pairs in there, got that 7th one “for free on the cheap.”
by PoopMongrual August 28, 2020