How much rent should i pay my best friend?

Hello,

I will be living with my best friend, her husband, and their 2 year old. It is a 4 bedroom house that's 2400 a month. I have one of the small bedrooms, access to one of the guest bathrooms that i keep clean, and very limited access to using the kitchen. I do a bunch of free babysitting. Edit: and cleaning, buying toilet paper and papertowels for the house, sharing my food, etc.

I can find a studio near me for 700 dollars a month including utilities and internet. My best friend and i are going to talk about how much rent i will be paying but i would like some reference as to how much is reasonable first. How much should i be giving a month considering everything in the post?