What a wonderful question! First, look at your experience. What are your transferable skills for jobs in nonprofits. I would expect that you have many. You can support an agency by working in IT, admin, or project management. But it sounds like you want to work directly with poor clients and provide services.
Personally, I care about foster care youth and services that assist them. Do you have a particular cause you care about: domestic violence, homelessness, veterans, children, ex-offenders (youth in juvenile justice)? If you know you can search agencies that serve that population.
Or you can search for jobs based on title: case manager, advocate, program assistant, counselor, etc.. The jobs pay dramatically different from agency to agency, job to job. The average direct client service job, entry level without a MA or MSW, would be $9-$16/hr.
Nonprofit jobs can be found at: