When I read the title of this post, I thought the end of the story would be how you had to spend $700 replacing some other component (like a catalytic converter, or a used head) as a result of the clogged air filter...thank God it was just wasted fuel.
Based on our gas reciepts, it takes our household about three months to consume $700 of fuel! That's with my wife and I switching back and forth driving ALL THREE of our MBs!
So either you are in a country where gas is super expensive, or you lived with this problem for a loonnnnng time...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car