Prices of cameras and lenses in Hong Kong are among the cheapest in Asia. The shops get lower dealer prices than elsewhere because they buy their goods in larger quantities (thanks to the huge china market), therefore, they are able to sell cameras at lower costs.

General Guide:
Avoid shops at touristy areas (e.g. shops in Nathan Road at the Tsim Sha Tsui area of Kowloon).

Instead, visit the shops at Sai Yeung Choi St. and Tung Choi St. at the Mongkok area of Kowloon. (i.e. Mongkok subway station D3 Exit).

Here's an unofficial, but pretty useful list of camera & lens prices in Hong Kong

Here's a list of good places to shop for camera stuff in Hong Kong.

1. Tin Cheung Camera (天祥)
phone 2722-1265
Shop 5 Friends' House, 6B Carnarvon Road, TST, Kowloon, Hong Kong.
尖沙咀 加拿芬道 6B 號 集友大廈 5 號舖
Note.... they charge you extra 3% if you want to use credit card.

2. Man Shing Camera (萬成)
phone 2396-2996
G/F, Shop 106, Tung Choi Street, Mong Kok, Kowloon, Hong Kong
旺角 通菜街 106 號舖地下

3. Wing Shing Camera (永成)
phone 2396-6886, 2396-6961
G/F, Shop 66, Sai Yeung Choi Street South, Mong Kok, Kowloon, Hong Kong
旺角 西洋菜南街 66 號舖地下

4. Kowloon Life Camera (九龍生活)
phone 2384-9302
G/F, 5, Woosung Street, Yau Ma Tei, Kowloon, Hong Kong
油麻地 吳松街 5 號舖地下

5. Zhao Xiang Guan (照相館)
phone 2722-0068, 2722-0161
Shop 501C, G/F, Kimberley Hotel., 28 Kimberley Road, Tsim Sha Tsui, Kowloon, Hong Kong
尖沙咀 金巴利道 28號君怡酒店商場地下501C鋪