Hamster chewed on my bathroom door, what can I do to fix it?

We have a pet hamster that we keep in the bathroom. The problem is that sometimes she gets out of her cage. During her last outing, she decided to chew on the bottom of the bathroom door. There are now little gnaw marks all along the bottom of the door.

What should I do to fix this? Do I have to replace the entire door? How much does it cost to do this?