Calculating total outgoing transaction fees associated with a single address?
The API blockchain.info provides for the address details does a ton of processing at it's backend (by accessing the blockchain for which they must have maintained a separate db for quick fetches). As far as the transaction fee is concerned, it can be calculated by finding the difference in the inputs and outputs of a transaction. This is somewhat tricky because the vin (input) for any transaction points to the output of another transaction. But the point being you can find the difference and the transaction fee.

I suggest you query the blockchain using the core Bitcoin API and maintain your own database as per your convenience. The blockchain.info API is kind of a dependency for the app and if their server goes down, so does your app. So maintaining a custom formatted data on your side is a good way to go and also ensures responsiveness.