And they do. There have often been a group of snorkellers with us when we went out to dive the Blue Hole. They get dropped off at different spots too when we dive the followup dives.
I've never checked into the snorkeller's price. I can't imagine that it is all that much less expensive because the amount of gas used to get them out there is the same, whether taking divers or snorkellers.
That said, I've had some really nice snorkels during surface intervals, while out at the Atolls.