Learner's definition of EXTRA
1 always used before a noun : more than is usual or necessary
a sandwich with extra mayonnaise
She got a part-time job to earn some extra money.
He gave us an extra week to finish the job.
There's no extra charge for breakfast.
Room service is/costs an extra $5. = You have to pay an extra $5 for room service.
2 : costing more: requiring additional payment