Do not be fooled by universities who offer a large stipend and then demand expensive tuition. But not until the 2nd year. When you receive your letter of acceptance, it will specify the exact compensation. As your career advances, you can improve your financial situation by finding special opportunities to collaborate with off-campus laboratories. This can be quite lucrative, and it is an excellent opportunity to see what industrial Ph.D. scientists do.
Similar opportunities exist in government labs.
For example, if you were to enter into a collaboration at the National Institutes of Standards and Technology near Washington, DC, you would typically receive the per-diem rate to support your stay there. You can retain your stipend AND add teaching to supplement your income. If your performance suffers due to excessive teaching, we will point that out. Apprenticeship is a short period in your graduate career during which you will work directly with a senior investigator, usually your research advisor. It is needed because, in traditional graduate education, your advisor spends a lot of time finding money for your support.