How much should I pay my sister for babysitting?

She’ll be watching him five days a week, 6-8 hours a day, every week. I’m not exactly sure what would be a good amount to pay her. The thing is I won’t have a whole lot of money which is why I asked her to watch him in the first place, I can’t afford daycare. I’m struggling so bad rn and I’m thankful she even offered to watch him so I want to make sure I pay her a fair amount.