OMG, you can't leave off Homecoming by Cynthia Voigt! Teen girl and siblings get abandoned by mother in a parking lot, have to live off of pennies until they find grouchy aunt who doesn't want them anyway.
I also remember the Ramona books focusing on money quite a lot. At one point, Ramona is sick and her dad has to take her home in a taxi. She starts freaking out that she'll throw up in the expensive taxi. It was the first time that I, as the child of fairly well-off parents, was able to envision how stressful it might be if your parents couldn't afford everything you needed or wanted. Probably had an enormous impact on my life going forward.