Is there a vitamin deficiency that causes leg pain, cramps?

It is possible: Low vitamin d levels can cause muscle pain and weakness. Studies show that as many as 25% of people with fibromyalgia and chronic fatigue syndrome have low vitamin d levels, and that supplementation may help lower pain levels in some cases. One study shows that vitamin d-deficient people need twice as much narcotic pain reliever as non-deficient people.

Magnesium also: This isn't really a vitamin, but magnesium deficiency is a common enough problem for me to mention it here. For this you want 2:1 calcium in combination with magnesium -- say 300mg ca with 150 mg mg. You don't want a huge amount of mg because it could produce diarrhea otherwise.