How to get an underwater 'case' for my camera (for underwater photography)?

I really want to get into underwater photography and i have a DSLR Nikon D3100, and i want to get a waterproof case. I don't know much about what works and how much they cost.could someone please give me a hand with this?

Well, if you want top notch professional equipment, how about:
http://store.aikotradingstore.com/ik68uncahowa3.html

A (much cheaper) variant might be:
http://www.amazon.com/...B002UDZZK0

There are different types. For something you are only going to use occasionally you could get a Dicapac Underwater Bag for around $150. You can spend megabucks for a hard case… Something like the Ikelite could cost as much as $1500 but I've seen a few cases for around $500.

edit:

One thing I would add is you need to talk to the experts before taking your camera underwater… And in this case, the experts aren't the people in the camera shop, the experts are the guys in the scuba diving shop. You need to be really careful with seals, you need to check and recheck them every single time you use whatever option you go with.