Used to be walk up $5 when the kids were away for the Christmas holidays, but even if it still exists, I'm guessing it's more like $10-$20.
I don't ever recall it being done online. Granted, it's been 8 or so years since I got there early enough to stand in line and get them for $5. Nor do I recall it being available on Thanksgiving as the kids tend to stick around more this week than between semesters.