Google makes Feedburner Pro free. They need to start integrating this stuff with Google Analytics really.
PRO is feed analytics taken to the next level. You will now have access to the number of people who have viewed or clicked individual content items in your feed and “Reach,” which estimates the daily number of subscribers who interacted with your feed content. You can turn this on by signing in to your account, navigating to the Analyze tab and heading to the FeedBurner Stats PRO section. Click the “Item Views” checkbox to activate these PRO features.