How much to pay for teen cat-sitter?

[magur]

Hi, we're planning a 2 week vacation and were wondering how much we should offer to pay for someone (a teen) to look after our 2 cats. We'll ask them to come in once a day to make sure they have food and fresh water and clear the litter box. He'll also need to replace the litter twice a week. We're only planning to check with someone close by - either next door or a walking distance away.
How much would be fair to offer?
Thanks