Daycare help!

Posting anonymous incase my cousin is on here 😊 and sorry if this gets long πŸ˜…

I am a stay at home momma with a 12 year old, 5 year old and almost 2 year old.. as of right now I'll be getting my older boys to and from school on Tuesdays and Thursdays

My cousin has recently started looking for a new babysitter for her 2.5 year old and I am debating on offering to watch her.. she needs a sitter Tuesday-Friday from 7:30am-5pm

My hesitation comes from a previous family babysitting arrangement I made years ago that was a complete nightmare with my uncle and his wife.. I was way underpaid and felt I was an on-call sitter.. (neither party has hard feelings after I stopped watching their daughter but I don't want to put myself in a similar situation) with my cousin I'm not worried about her overstepping the situation like my uncle and his wife did.. but if I offer I also want a number (as in pay) to throw out as I didn't do that the first time and I worked for basically nothing (which it isn't about the money.. I wasn't and still am not offering or thinking to offer help to make bank from family.. but I also don't want to do it for free or for $1 per hour like last time.. I was previously receiving $150 per month watching for my uncle usually between 3 and 5 days per week *usually 4-5 days* from 6:30am-4:30pm)

So what would you charge for 4 days a week for roughly 9.5 hours? What's a reasonable price to charge per month also if it's for family if that makes a difference πŸ€·β€β™€οΈ.. again I'm not looking to make bank off watching her daughter but I'm also not wanting to watch her for free either if that makes sense..

Any help or advice is appreciated!