The existing "approved" meds for MS do not come with a guarantee of actually helping the disease; in fact, their efficacy is only about the same as placebo in studies. Personally, I don't think doctors can find an effective med until the cause of MS is known. I have chosen not to use any medication for that reason, even tho my insurance does cover it.
Therefore, my advice is "Do not panic if you feel you cannot afford the meds. Perhaps they are not doing any good anyway. If you feel they help you or you must take them, discuss the situation with your physician. There are programs through the drug companies to help."