I decided that knowing how many gallons it would take when the light comes on is more worthy information than how far I can go with the light on (since I always carry DEF with me).

So I went to the car wash (so I could rinse off any potential spillage...) and filled it up to the rim.

5 gallons of Def. $28 after tax @ my local autoparts store.

It took ~4 gallons to fill it.

8553miles/4 gallons = 2138 miles/gallon.

$28/5 = $5.60 gallon

Conclusion: The consumption of DEF over 1000 miles costs less than a gallon of diesel.

Average fuel fillup: $80.

Average fuel range: 400 miles

8553 / 400 = 21 tanks of fuel used over 8553 miles.

21 tanks of fuel costs: $1710.60

So for every $1700 I spend on Diesel I spend less than $28 on DEF which is waaaaaay less than I spend on RedBull over the same amount of driving

i.e. non-issue.