lph, I had the exact same problem a few years ago when skate skiing. Ball-of-foot pain that then became arch pain, only in one foot. It turned out to be the insoles. I got some green Superfeet insoles and swapped them out for the ones that came with the boots, and that fixed it.

In my case the boots were new, and one foot just needed more support than the boot provided. If your boots are old, I'd bet new insoles will help, since the insoles break down over time. Hope your foot feels better soon!