Question about Babysitting?

Lakin • Wife💟Mother☮️Christian✝️ 🎀💘Arbor Jade 7/18/19👨‍👩‍👧🌺

I am a SAHM with my July baby and currently 22 weeks pregnant. Before I had my little girl, I babysat three older girls ages 7, 11, and 12. My husband owns his own business but also works at an addiction treatment center as we are both in recovery. I’ve been sober almost 3 years and him 7. He came home the other day and told me he had volunteered me to babysit for one of his peer mentors who just had a baby. The baby is only two months old. I don’t mind to watch her until around Christmas as I am due in January. My question is about what I would charge? I feel like I should not charge much as the baby’s mother and father are both in recovery as well and don’t make much money but are trying to do right. But I don’t want to do it for nothing either as I’m sure it’s not going to be easy being pregnant with a toddler then having a two month old to watch? Any opinions? Any money would be extra money for us that I will probably just use for Christmas presents.