My cruise to the Bahamas just got cancelled for the 2nd year in a row and I am thinking about just cutting my losses and going on a dive trip to Cozumel.
I love the idea that "cutting your losses" means a trip to Coz. I'm going to adopt your outlook on life... and work on cutting my losses more often.
I know you can book travel with PADI and I'm curious if it's really a money saver or if there is any particular advantage.
Booking directly with dive shops, most of which can also arrange a package deal for lodging, is pretty simple and effective. I'm not sure if PADI travel offers an advantage, as I've never booked through them. But it's likely you can check out the comparative trip directly from the operator (dive shop, resort, etc) and if there is a difference in price you can decide if it's worth it.
Is it generally cheaper to book dives ahead of time, or is the price pretty much the same regardless?
I'm going to say "pretty much the same, regardless." By that I mean if you reserve 5 days of diving, one dive trip each day, in advance, you will often get a "package price" for those five days. If instead you show up, dive one day and then the next and the next... for five days... you will usually also get the package price.
If I'm going for a week (as I am next week) I typically book in advance one two-tank trip each day. I think this gives the dive shop a plan to work with, and they understand the plan could be modified as the week progresses... some days we'll add an afternoon or evening dive trip, or another day some in our group might have to sit out a day of diving. Every shop I've dived with in Cozumel seems to understand this and has been very accommodating... charging me at the end of the week for the diving we did.
Novice question also, if I go for 7 days, it says I get 10 boat dives. Are you generally doing 2 dives a day?
Probably arrive the first day, dive for five days, leave on the 7th day... 7 days/six nights, one dive trip each day for the middle five days.
I know it's supposed to be diving trip but I'm a little worried I won't have the stamina and will want to relax more at the hotel beach and snorkel.
Cozumel diving is pretty relaxing... drifting along, enjoying the scenery. Snorkeling might be more work. And after your first day of diving you'll likely re-evaluate any desire to snorkel anyway.
Sounds like you're heading in the right direction (i.e. to Cozumel.) You'll have a great time, and you'll be well taken care of, regardless of who you book through.