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What about a cache file like on Slacker Radio? When connected to WiFi you can cache your station so your not streaming from LTE all the time while listening
 
There's a lot of threads where iTunes Radio data usage is reported and discussed. The first one I grabbed states around 38 MB per hour. Doing the math, 10 hours per day is 380 MB and two weeks of that is around 5 GB. Nothing in life is free.

I'm not clear on if the OP had a data usage estimate on iOS 7 without iTunes Radio. Comparing data usage of a beta against a released iOS version is apples (ha) and oranges.
 
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