Been driving 144 miles round trip to work for the last two weeks on 2 lane curvy/hilly state roads with speeds between 55-70 and have gotten 29.02mpg at both fill ups. I'm at 2650 miles with only 19% of my DEF left which bothers me some.
At 8400 miles I have 12% DEF remaining. That makes my DEF consumption a little more than 1% for each 100 miles driven. If you are near a truck stop you can buy DEF at the pump for less than the jugs at stores.
My dealership throws in def refills with the free provided oil changes and the first 3 are free, so that is one thing you can check out when purchasing. Also def at the pump is around $2.50 at least for around me and I have been told that def at the pump is better than the jugs, because if they get too hot or cold it messes up the def, which can mess up your whole system.