I lost hair by the handful when I was on pred and 6-MP the last time. There were quite a few days that I cried in the shower. At first, it seems like I lost a lot of hair really fast, but then the hair loss leveled off, and eventually it grew back. I took a two pronged approach to mitigating the hair loss: a) nutritional supplementation (Biotin and Walmart's own brand of gelatin tablets) and b) making the hair look more full (Nioxin and hot rollers).
The only thing I stuck with in the long term was the Walmart Gelatin tablets (Nature's something?... it's obviously their house vitamin brand). They are dirt cheap, help your hair and nails grow, and I think that gelatin helps to prevent the collagen loss that occurs in skin when you are on prednisone.
I hope that you can find something that works for you!