Just having a strobe makes a big difference. Try to buy a "kit" used that already has a strobe.
Doesn't need to be big or very powerful - however - no matter the camera quality, it's the strobe that makes a good picture.
Of course for macro this doesn't apply; you're so close to the subject. But to get a nice shot of tourists with a reef background & fish, the better the strobe, the nicer the depth & the colors would be.
Don't be surprised that the strobe costs the same as a camera + housing, or even more.
On ScubaBoard, in the photo sections, look at posts done by other users. They state the equipment that was used. If not, I ask them to!
Should give you a general idea.
If you're going "new" then consider the Micro 4/3 cameras; Olympus has a good line, Panasonic too. Both companies sell their own housings; however you can find Chinese clear plastic knockoffs for cheap, they just have a lower depth threshold.
A 4/3 setup will be more expensive than a Canon S95 + housing, but will be more future-proof. Interchangeable lenses.
What I do NOT recommend is using a single camera for both video & stills; switching between the two UW can be a pain, and as a DM your focus should be your wards - not the camera. So keep it simple.
Most *for sale* on SB are in the US; so shipping will cost you dearly. Try to find locally. A dedicated camera store might not have in stock but can order.
Do your homework, and come back & say to us, "I have narrowed it down to these choices..."
AND
if you SEARCH, you'll find such threads already, quite recent.