This is a good link/guide to buying cameras in Hong Kong: http://rolandlim.wordpress.com/2007/...-in-hong-kong/.
We bought the camera from DC Fever, which was cheaper than the other shops (sometimes you have to walk around shop to shop in Mong Kok and ask for the prices). They threw in a bunch of free stuff, too, like the camera case. DC Fever is not directly on the ground floor, hence, their prices might be a bit cheaper. So, we've had a good experience there.
You could also look at the computer center in Wan Chai (good prices quoted there, but never bought there).
My partner said you might have to shop around to see which shop has a particular offer/better price for the model you want at the time. Don't shop in TST, and buy from a store that actually has a name, and NOT from a store that claims to be "tax free". <ok, end of advice from my other half>