I don't know what the norms are in econ, but a student couldn't get a B+ in my courses without ever showing up. I'd just add that the strategy of doing the rock bottom minimum might sometimes yield okay results in university, but it is not well received at all in the world outside university. I think riotior will do very well to break that habit.
I had horrible attendance in one of my classes this year, probably because it started at 4:30. At any rate, I have a lot of students who are going to get Ds or Fs. Some of these students, who've missed a good half of the classes, are now e-mailing me to see if they can do some extra credit to get their grades up. It's hard to understand the mindset of people like that; clearly they want good grades, but why didn't that motivate them to come to class throughout the semester? It's like religious people who live shitty lives and then think they can make it all good with the Lord on their deathbeds.