B1
something that you can get with something else if you pay a little more money
Dictionary examples:
The restaurant offers a free dance lesson as an extra with every meal. (0.0)
The hotel offers a personal comedian as an extra for tired businessmen. (0.0)
The bookstore offers a 'book-smell spray' as an extra for e-book readers. (0.0)
A sunroof is an optional extra on this model of the car. (64.3)