The dive ops are priced competitively on Grand Cayman, especially if you stay on the Seven Mile Beach and contract with an off-site operation, so check for specials and packages, you might get lucky. Some of them will pick you up on the beach with a boat or by road with a van.
Some of the smaller operations might work out a special price for you; check with Cayman University Divers. I am not familiar with Ambassador Divers, but most Cayman dive ops are good and they may have options for you if you ask.
And there are a few diver-dedicated hotels with onsite dive ops that may be more economical, it depends. Some offer 2 boat dives per day and then unlimited shore dives on the house reef and that may help with the price and they include easy, onsite gear storage. But these places are "off the beaten path" and you may need to rent a car to see more of the island - but there is a lot more to see besides the 7MB and Georgetown. I recommend renting a car anyway.
Some of the diver-dedicated GC hotels with an onsite dive op include:
- Compass Point offers East End diving but you are pretty far away from all the other island attractions, but you can get 4 boat dives a day.
- Sunset House is South of Georgetown they offer a mix of boat dives and shore dives and I think it includes breakfast (but I've heard that the house reef has gotten beaten up but I don't know.)
- Cobalt Coast is north up near Hell and they offer an all-inclusive stay that offers meals, 2 boat dives, and unlimited shore dives (weather permitting)
- Lighthouse Point and Holiday Inn are north side locations with an onsite dive op with boat and shore dive options
It's not Bonaire, but there are also some good, independent shore dives ops available on GC, so you could plan to do some boat dives and then go off on your own to shore dive to save money. For instance, Sundivers is the on-site op at Turtle Reef and you can rent a tank and weights for $15 CI to dive from shore. Again it is helpful to have a car if you plan to shore dive.
If these options don't appeal to you, try reaching out to the dive ops to ask them about packages for diving and accommodations. Or ask the Comfort Suites about dive packages. I've stayed at Comfort Suites and it is fine but nothing special IMO, so you may be able to find something better, just my opinion. Look at Sunshine Suites and DiveTech, they will pick you up but the resort is across the street from the beach.
You might also look beyond Grand Cayman to the sister islands where many feel that the diving is better, but these are quiet, rural places without much night life. The Cayman Brac Beach Resort is a small, diver-dedicated resort and the price includes transfers, food, lodging, valet diving, hotel service charges, taxes, and some of their packages include drinks; so everything is covered but the dive shop tips. It will cost you about $140 US for a round trip flight to Cayman Brac or Little Cayman.
And if you want to do a lot of diving in the Caymans, look for a good deal on the Cayman Aggressor liveaboard. All your costs are covered and you can do 4-5 dives a day at the best sites off of all 3 Cayman Islands (weather permitting). It may seem expensive but you can do a lot of really nice dives and if you work out the costs per dive it may be more economical.
The Caymans offer great Caribbean diving and there are a lot of options to consider, have fun whatever you decide!