The P2P Subscription Sales module excels at this type of analysis. All new and renewing subscribers are tracked by source code so you will always know the cost to acquire or renew all of your subscribers.
You can reduce manual data entry by linking your website order page to P2P. Credit card orders will be processed automatically and all subscription orders will be seamlessly integrated into your subscriber database. Your subscribers will be able to manage their own account to change address, renew a subscription, etc.