If you don't want to spend a fortune I'd say go for a cheaper camera and spend some money on lighting and flash. If you only dive while travelling a smaller camera is to preffer either a camera like the Sony rx100, or maybe a mirror less.
You can use one or two flashes or only light's (but light's might scare some creatures of) but if you also want to take some films lights are a big benefit.
I started out with a Canon S95 with only lights, then went over to a NEX 5 in a Nauticam housing with two lights. Latelly I have added on one flash, having two lights mean I get some help on the side where the flash is not lighting up and it has worked pretty well, but I now added also a second flash, but have not yet used that setup.
You can see some examples @
https://www.flickr.com/photos/tomas_woren/sets/
Lipe 2012 is shot with one light and a canon S95 (some with Nex5 in a Meikon housing, but it did not work under 15m so had to use S95)
Bali 2013 Two lights Sony nex5
Thailand 2013 and later Sony nex5N two lights and one flash.
Weight might be an issue if you go for an Aluminium Housing, my setyp with Nauticam housing for Sony nex5N and a "4 dome port, diopter holders, two lights and a flash adds up to 9kg so a bit too much to bring on to most flights as carry on, but so far I luckily not meet no problems doing so :cool2:. A flat port with wet lenses is likelly a lighter option, where you with some risk to loose the wide angle shooting for a trip could put the wet lense in the check in luggage.
Once I get my new housing for Sony a5100 I'll have a housing and camera set for sale
(but you need to add on ports and zoomgear)