Typical boat dives on Grand Cayman are a deep dive followed by a shallow 2nd dive. So you could be looking at a 100' dive followed by a 40' dive. If you wanted to sit out the first dive, you could just do the second ones. I think most of the diveops would only charge you for 1 dive, they're pretty flexible with their pricing due to competition. Here's max depths (off my computer) for all the 2nd dives/shore dives that we did.
Turtle Reef - 59' shoredive. Easy entry down some steps into a protected cove then a short swim out to the mini-wall. A lot of it was 40' or less.
Peter's Reef - 48' boatdive
Aquarium - 42' boatdive - this was an outstanding dive - thousands of fish.
Governors Reef - 49' boatdive - disappointing site though.
Mermaid at Sunset House - shoredive 53' standing next to her - easy entry.
Eden Rock - 38' shoredive, and we had to work hard to get that deep, alot of it is 25' or less. Although it's beat-up since it's the closest divesite to the cruise ship port. Best part of this dive was a group of Eagle Rays that went screaming over our heads.
Stingray City, most fun you'll have in 15' of water. The Stingrays have learned to give you a "kiss" to get you to drop the squid you're feeding them, it can draw blood so beware of that. If they don't smell the squid in your hand, they ignore you though.
You might also consider Bonaire. Most of the dive resorts or condos on the water have big wide steps off their divedock for easy access. I was filming there w/o lights so I had to stay above 60-70'. Most of the good stuff starts in 20-30' just about everywhere, the dive profile on most of the west side is 20-30' to about 120' max if you go over the drop. But I almost never did and still had some fantastic dives. Not a lot of big life on Bonaire though, an occasional ray and some tarpon is about all. The coral and sponges are spectacular though, better than Cayman imho.
Most of the shore diving is over/through coral rubble and ironshore so you tend to get a little scratched up. But you could easily do 10 shoredives from the different resort docks. If you boat dive, you'd never have to contend with the ironshore/rubble entries. A lot of the divesites are either/or, there are times that boatdivers see shoredivers at the same site.
Here's a depth list:
Jeff Davis - 49' boat
Witches Hut 56' boat
Cliff - 40' shore - from Habitat's dock
Bari Reef - 15-50' from Sand Dollar's dock - we did a REEF fish survey there and counted around 100 different fish species in less than 30', saw a few squid also.
Salt Pier - 48' at the bottom of the third set of pilings. The first two where we spent most of our time couldn't have been 30' And it's a great dive, lots of interesting things growing on the pier structures. It's kind of a sandy beach entry over some ironshore though so might be done better from a diveboat to minimize the risk.
You could easily do all your dives on Bonaire w/o ever breaking your depth limit. All the divesites we went to on the boat, with two exceptions, started out so close to land that it was 15-30' or less under the boat. One of the Klein sites, Jerry's Reef had a deep/shallow option depending on whether you went towards or away from the island. The best stuff we saw there were turtles under the rocks - in 15'...
It's pricier to get to Bonaire than Cayman but it's not so hideously expensive once you're there.
hth,
) Have done dives when OW students were on the boat,one group went deep,the students stayed at 50 feet. It worked fine but does need 2 divemasters.
