Welcome to ThisIsMS. As a graduate student, you probably won't be making a great deal of money. When I was in grad school I had a university provided graduate student health insurance plan (GSHIP). This was through Blue Cross. Enrollment in the plan was covered by tuition and fees. If you're supported by a lab on a PI's grant, then this should be covered. I was diagnosed with MS during my second year as a grad student and decided to take Avonex. I ordered it through the school's health center pharmacy and my copay for a one month supply was around $500 if I remember correctly (this was in 2000, prices have gone up since then). Due to my limited income as a grad student, I qualified for Biogen's financial assistance program and just had to buy the first month and then they gave me the rest of the year for free.
I hope that helps. Note that your specific case might be different since you'll be a foreign student. I'm not sure how that will affect things.