I don't think you can actually come up with a true "average" scholarship offer. It depends on many things-recruiting budget available, where they see the P in their rotation, etc.
A better question may be to look at and see what that particular school offers players and how the scholarships are split up on their roster. I don't know if the coaches will give out specifics, but they may say something like "we give 60% of our scholarship money to P's and the remainder to postion players" From that, you can probably figure out what you want to know.