What is the percentage by weight of meat in a split chicken breast?
The USDA NAL has this to say:


  Refuse: 20%   Refuse Description:   Bone


In addition, you can compare the serving size weight of the breast with skin (145 g) to the weight of the breast with meat only (118 g), each derived from 1/2 chicken breast, so the skin accounts for about 18.6% of the deboned breast and 14.9% of the bone-in breast (accounting for the earlier 20%).

All in, it looks like a bone-in breast with skin is slightly more than 65% meat.

Breast meat is generally the most expensive part of the chicken to buy, even bone-in; if economy is really a factor here than you really should consider using the whole chicken.