PhD's and Masters can be done for FREE in the US if one knows where to look and how to leverage on the opportunities. People in STEM field SHOULD NOT BE PAYING TO GO TO GRAD SCHOOL.

State colleges and Ivy League schools are usually the best options in terms of getting a fully funded program in the STEM fields. However, acceptance into these programs are highly competitive so acceptance rates are comparatively LOW.

It is even more competitive for international students. A fully funded program in the USA offers 100% tuition cover and could come with a stipend. Some offer out of state tuition waivers, meaning the student only has to pay resident tuition fees.

Given that PhD programs in the US could be anything from 3 to 5 years, its probably not a wise idea to commit ones own financial resources to the venture without any form of financial aid. 

Stipends are effectively compensations for services rendered to the university in the form of Graduate Teaching Assistantship or Graduate Research Assistantship. Go Here for more details on them. 

As you can see, grad school is mostly handled by each department, not the Graduate College. When you apply to grad school, you’re applying to the department, not the Graduate College. When you get accepted, the department recommends your name to the Graduate College and you get in.

Nevertheless, just because your tuition is waived, it does not mean you don’t have to pay anything to the school. You may still need to pay the semester school fees, student insurance, and other miscellaneous school expenditure.

There are many graduate programs (both Ph.D. and Masters) in the US that do not fund students. But my advice is not to go to these schools. The funding provided by the school and department, tells you how healthy the department is when it comes to research money and growth. 

Let me unequivocally state that YOU SHOULD NOT HAVE TO PAY FOR GRAD SCHOOL