Fountain Solution filter bags (exciting, right? right?!)

Quick questions. If you use a system like a Tresu Royse, you probably use filter bags.
- How often do you change them?
- What position (press operator, plant mgr, etc.) decides which filters to buy?

Bonus question if you want to share: roughly what are you being charged per bag?

Thank you. (Nope, this is not the opening to a fascinating filter bag sales pitch)