How much would you all charge?

My best friend had her second baby a couple weeks ago. Before he was born, I told her if she wanted me to, I would love to baby sit him if/when she decided to go back to work. She also has a 3 yr old daughter that I love like my own. I have a 1 yr old son, too. Well, we were texting last night, and she is going back to work in a few weeks & wants me to watch him & her daughter. No problem! I love them to pieces! I'm at stay at home mom anyways, but I would love to have a little extra income though. If she had to put them both in daycare, it would be at least $275/week. She said she'll pay me, but we haven't discussed a price yet. How much would you all charge? I talked to my mom about it, and she says maybe around $150/week. Also, my other question is for breast feeding mothers. She's breast feeding the baby, and she's nervous about me running out of it while he's here. She doesn't work very far from my house though, and they'll let her pump at work. I told her I have no problem with driving to her job to pick some milk up if I need to. How much breast milk would you all recommend she stores up? I know she can pump & freeze, but I'm not sure how much would be a good amount to do?