Hi, do you have rheumatoid arthritis? Even if it's not, if your arthritis is this severe, it poses a lot of questions for being pregnant. I'm guessing it is, because while I'm having to educate myself on the fly here, it sounds as though methotrexate is only used for a small subset of osteoarthritis patients (?).
Anyway, as you know, rheumatoid arthritis is an autoimmune disease, so that raises the specter of immune problems that might interfere with your getting pregnant and carrying successfully. Have you had immune testing? I realize it's controversial, but there are an awful lot of women here who feel that immune treatment is what made the difference between successful and unsuccessful cycles. You don't mention your ttc history, but have you had a lot of failed cycles, OE or DE?
Second, I was pg in my late forties, too, and I have mild osteoarthritis. So, I can tell you, adding forty pounds or so to your body is a definite stressor on your joints. In addition, I developed edema late in pregnancy, while led to my getting peripheral neuropathy in my feet (as well as CTS in my hands). The CTS resolved, but the peripheral neuropathy never has totally, and when combined with the arthritis, it can make life pretty unpleasant. So you need to think really hard about whether carrying a lot of extra weight is going to be manageable for you.
Finally, I agree about researching alternative therapies, and I'm a bit reserved on them (not that I don't use any). In your situation, I don't think you have anything to lose. Methotrexate is pretty nasty stuff independent of your desire to ttc. But you also will need your joints to be in good shape to handle the rigors of new motherhood.
I'm sorry you're getting such difficult news. Using a GC is a huge expense if it comes down to it, but at least you have frosties.
Maggie (in VA)