Nitrox is free to students.
Nitrox is $10 per tank no matter what size (AL80, LP95, Double 100s).
Nitrox is $5 per tank (again, regardless of size) if you're a dive club member ($40 a year).
That means, nitrox from the shop I frequent is 1/4-1/2 the cost of anywhere else I get fills.
I read that as you are saying Nitrox fills are $20-40.
I get my HP tanks filled from the banks (32) at Aquarius Del Monte for $10. I think LP
tanks are a little less ($8?).
AWS charges $10 for a Nitrox fill from the banks (32) by the each, $8.50 if you get a
Nitrox fill card.