Sorry to hear this. Depending on the square footage of the roof(roofer square) you can expect to drop 6,000-10,000. Hopefully not more. Get several bids. Go to certainteed's website see if there is a certified roofer in your area. Make sure you get a bid from him.
If it makes you feel any better. When i had a new roof put on my house 3 years ago. The whole roof needed to be re sheathed. 82 sheets.
I went with osb at 30 installed. Even though i like 1/2 inch cdx. Which was 50.