Intova has a line of budget priced digital cameras that come with dive housings. I`d purchase the highest pixel rated 1 that fits your budget.
They also have a external slave flash that works with virtually any digital or film camera that has a built in flash. It comes with tray, flex arm, underwater housing and accessories and can be found on the internet for about $100 The only thing it doesn`t come with that you`d need to hook it up is it`s fiberoptic trigger cable that runs $10-20.
Intova even makes a set of filters that fit the ports of their camera housings.
Although I don`t have one of the Intova cameras I do have 2 of the flash units. I`m very happy with them they seem to be exactly the same as the Fantasea Nano but priced much less expensive.
The reviews I`ve read of the cameras are good and considered excellent values for the models of 5mp and higher. I`ve seen the 6mp model priced $199 and as I stated that`s with a housing. I just also saw an add for a higher resolution model a few days ago. Some searching and research may be needed.
Good Luck!