As I am a student and I have other expenses, I don't always have the money to make bulk purchases of diapers, so sometimes I am frugal with the amount I go through in a day. That being said I don't always have the time to go into full baby mode either, so things do balance themselves out a bit.
When I regress and play I go through about 2-3 diapers a day. If I only plan on wetting for the day, I go through about 2. If I am deep into baby-mode, I'll bite the bullet and use a 3rd for wetting and messing.