Afaik, the threshold above which you do not qualify for any aid if you are an American student is a family income of $150K. If your income translates to less than this you may qualify for consideration, but I do not know if the same income limits apply for foreign and domestic students. Financial aid is awarded on a sliding scale.
Unless he is a citizen or legal alien he will not be able to get a 'work study' job (or any other job either afaik) while in the US. I don't think student visas allow students to work but I may be wrong on this .
American students who qualify for financial aid mostly receive institutional aid (a direct write off from their university). Students below certain income levels may in addition qualify for federal and/or state programmes. Work study is a federal programme available only to legal aliens and citizens. Other federal aid programmes are Stafford Loans and Perkins Loans (repaid after graduation and with a fixed interest rate iirc), Pell Grant (a direct award of money iirc) and programmes earmarked for certain categories of students like servicemen and women. Many students make their way through university with a combination of institutional aid, federal loan, part time jobs all through university, private scholarships, and private loans. A lot of American parents refinance their mortgages or take out loans. Taking out a loan on the US side would mean having an American co-signer so this is probably not realistic for you.
Some US universities offer generous financial aid (essentially a write off of tuition and/or room and board) to well qualified applicants from outside the US:
www.usnews.com/education/best-colleges/the-short-list-college/articles/2014/09/23/10-colleges-that-award-international-students-the-most-financial-aid
Some really good universities here and some I have never heard of. However, I wouldn't rely on lists on the web -- lists tend to be incomplete and sometimes contradictory. Call the financial aid offices of the universities your DS is interested in and talk to them directly.
Postgrad financial aid is harder to come by for foreign students in the US.