hiram,
It sounds like Lipitor is not the cause of your foot problem. The flat footedness is probably straining those ligaments.
Invariably a foot doctor will prescribe an orthotic device (they ALWAYS do

), but maybe before that expense, you might try a couple weeks with ibuprofen 4 times a day. See if that relieves the pain.
The blood tests for muscle damage will reveal the most serious conditions like rhabdomyolysis, and muscle necrosis, but lesser myositis or myalgia will get beneath the radar.
But it really DOES sound more like an inflamed tendon or ligament to me.
Have you tried daily CoQ10 which is always a good idea with statins.