Its about 10%. My computer was $2600, ram included. I can get AppleCare for $244 which also covers my ram. 2600/244=10.65%
from store.apple.com
MacBook Pro - AppleCare Protection Plan
Found in: Shop Mac > Mac Accessories > AppleCare
$349.00 Ships: Within 24hrs
Free shipping
This is for the MBP 15" or above. Even if I buy this for a high-end 15" MBP with price tag $2199, it's 15.9%. If I choose the base config ($1,799) it's 19.4%.