Anubis,
Expect to pay in the order of $1.5k - $2k for a housing. Disgusting price for a piece of plastic and few o-rings really
On top of that, you will be wanting to add on at least one strobe, more likely two. Nother couple of $K for that. Having said that, Ive never done any UW with digital, so its quite possible that the ability to bump ISO will give results that werent possible without strobes on film. Due to the light filtering, usually the only way to acheive any true colour and pop is lighting with stobes. You can also do some PP filters in
PS as well which tone down the blue/green and pull back in the reds and oranges (which get filtered first as you get deeper).
You will find you will need your full mind on the job for the first 20 or so dives, so I would suggest leaving the camera at home at least for the first few dives after your OW.
When you are taking photos, dont forget to keep up your buddy awareness. Also, work hard on your bouancy skills. You'll need them and also, there is nothing worse than watching some photog climbing around a reef on his hand's and knee's destroying things.
Another option might be to see if you can find a 2nd hand NikonusV, which is a dedicated underwater film camera. We can often get them here in NZ for ~$500 with strobe.