Going strictly by ear, you could remove the "by" from the second example and put it in the first, and both would be well understood; but neither would sound as smooth or as professional. The other differences which may contribute to this are, the second claims to be exact while the first does not (although quoting to the penny), and in the first, the "a barrel" is appended to the drop, while in the second, it goes with the final price. To me, it's mainly a matter of smoothness.
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