Out of curiosity I just took a look at the rates for a 14 night dive package at Cocoview in Roatan in September 2018 because Roatan is generally considered an economical Caribbean dive destination and CCV has a reputation as a good, mid-price, all-inclusive dive resort.
The 14 night package for CCV in September is about $2500 plus $475 tax (total = $2935, the rate varies a little with the view) and that includes food, diving, accommodations, and airport transfers; so it is around $1000 cheaper per person based on double occupancy. There are also a few extra fees for "special" dives.
So CCV is definitely a less expensive option but upon further consideration it might not be quite as much of a bargain as it seems. It is often easier and cheaper to get airfare to Cayman from the US than to Roatan - or at least that has been our experience - so you might make up some money on the air transport to Cayman - but it depends, you could get lucky and find great airfare to RTB.
Regarding the diving, you can do two 1-tank boat dives per day at CCV, along with two 1-tank drop off dives on the house reef, and you can do unlimited shore dives on the house reef at CCV; so a lot of diving is available at CCV.
But this new (trial?) CBBR/LCBR combo also offers a lot of dives and they are all boat dives on multiple anchored sites off 2 different islands. The package also includes the CB to LC transfers along with the "special" dives. So you might expect to pay a bit more those diving options - although CCV is still a good deal. The Cayman resorts and CCV both charge extra for Nitrox.
The CCV and Cayman resorts all serve meals buffet style and all have generally good reviews regarding the food. Cayman is usually considered a more upscale and pricey travel destination - and it certainly isn't cheap! But you do get the valet diving service at the CBBR and LCBR, and that's nice.
I've said this before, but I believe that there are other "hidden costs" for trips to Roatan and they are the travel medicine expenses. We take the CDC's travel warnings seriously - with good reason - so before both of our trips to Roatan we consulted an infectious disease doctor and got vaccinated or boosters against infectious agents like typhoid and hepatitis, and we took anti-malaria medication before, during, and after the trip. It was pricey and our health insurance didn't cover much.
We also regularly used strong mosquito repellent on Roatan and took food and water precautions (and drank bottled water especially when away from the resort.) We have not found these precautions to be necessary in Cayman.
So in general I would say that Roatan's CCV is the cheaper option for a 14 night trip tha tincludes food and a lot of diving. The CBBR/LCBR combo is pricier overall but it might be a better value in the long run.