When I started technical diving in New Mexico, where we had to do our trimix blending on site, it was just plain horrible in terms of expense. We had to bring a lot of helium and oxygen cylinders so we could always cascade and have something with reasonably high pressure in a supply bottle . Even so, I cannot begin to estimate how many thousands of dollars worth of helium we vented into the stratosphere so we could get the pressure low enough to add the O2 and helium before taking them to the local fill station for topping off with whatever air they have there, at $10 per tank top off in recent years. (Nothing quite like paying $10 for that last 400 PSI of air in your AL 40 to get 50%.)
Since I got the booster, no one has vented an ounce of helium into the atmosphere--whatever you have left over from your last dive is your base for the next one. Then we top off with clean air we brought ourselves. I have no doubt that it has saved us thousands of dollars.
