Remarkably or exceedingly inexpensive (as in, even if you doubled the price, it would still be a good value). Primarily heard in UK, Australia. I got a brand new three-piece suit for 50 bucks—cheap at twice the price!
Very inexpensive, a good value for the money. For example, Pete got a $3,000 rebate on his new car-it was cheap at twice the price. For a synonym see dirt cheap.