DandyDon:
Planet ticket Lubbock to Coz mid june: $493 ea
5 nights shared Caribe Blue & 5 - 2 tanks trips: $434 ea
Airport parking: $18 ea
Cabs & Vans: $30 ea
DM tips: $50 ea or more
$1025 for 10 dives = $100+ per dive before we get into other expenses
Did not include food...
Many spend a lot more per dive.
"per dive" calculations don't normally take airfare, hotel, cabs into consideration.

I consider my "per dive" cost to be ONLY what I pay to the dive operator which is their fee + whatever I decide to tip.
As for the other comments on the thread, you guys made me laugh with the farm stories. My dad's a farm boy and got his license when he drove the tractor into town one day and went to town hall. They asked him how he got there, saw he drove the tractor and gave him the license. He was about 15.
It's a parental decision as to when to allow a child to get certified and unless I'm the parent then it's none of my business.
I have no problem diving with a group of mixed experience, including brand new divers. Where would we all be if nobody would have dived with us when we were newly certified? Or if divers with more experience don't want to dive with you now? And I've seen lots of divers with hundreds + dives who still have no sense of bouyancy. How many dives you have doesn't mean that much.
With a shop where the scheduled dives are appropriate for a jr diver, there should be no issue with a 10 yr old being on the boat. And I don't think that any reputable, small Cozumel dive op would put a jr diver on a boat with 5-6 other divers unless everyone new about any depth or other limitations in advance and were ok with it. Or, have a 2nd DM for the Jr and parent to dive a more appropriate plan while the rest of the group does a deeper dive. Either way, if you are that adament about not being on a boat with jr divers then let your dive op know that when you book. If they can't accomodate you can go elsewhere.