I take on epill an hour before arriving at the dentist's office, and then they gave me a second pill just before we began. Like he said, "We discovered one works well, but two work better."
They would hook me up to a blood pressure machine and something else (I forget what it was for) to monitor my vitals throughout the procedure. Apparently, they would also wake me periodically, but I don't recall that happening much. I know there were brief periods of time I'd be "aware" that they were doing work, but it never lasted long.
My co-pay for the pills themselves was only $10, I think. But there was a charge for the extra person in the room to monitor my vitals at all times. So, yes, that's what made it expensive... but it was well worth it to be blissfully unaware of everything going on around me.