And to decipher what Steve said
... NLE means "editing program" such as Abode, Sony, Mac etc
As you are a Mac guy Alex you would go with Final Cut (i think there is a "light" version that doesn't cost 3 children) or imovie to start
Big 4 manufacturers for UW vid tend to be Sony, Canon, Panasonic, and JVC.
Sony has by far the biggest part of the market and most housing support. Like Nikon in film days. Sony also has a control that allows for electronic push button housings, i am not sure but i don't think the other 3 do?! The other 3 are therefore manual controls on the housings. (I think there are some exceptions there?!)
There are 1 chip and 3 chip cameras in the consumer/prosumer market, 3 chip has the better colour. You want a camera and housing combination that can manually white balance. That knocks out a lot of the lower end cameras.
So, depending on what you want there is not a huge selection of middle range stuff that is reasonably economical. To get a camera that has all the controls etc you want, then you have to spend the money. 4 to 5 grand and it will be big.
If you want a smaller unit to have fun with and take along with you on a trip then there are several choices, HC series from Sony and HV series from Canon.