Jack Moved from New Hampshire to Florida and Decided to Have

Jack moved from New Hampshire to Florida and decided to have an air conditioner installed in his car. After it was installed, Jack received a bill for $1,200. Jack called the dealer and told him he'd never heard of this service costing more than $500. They argued, but the dealer finally agreed to take $900. Is the agreement enforceable?

A) Yes, there is no way for the dealer to get the extra money anyway.
B) Yes, there is consideration for the modified amount.
C) No, there is no consideration and the dealer can sue for the extra $300.
D) No, there is an implied contract to pay the dealer whatever he billed Jack.