In my experience, at that price range you are probably better off buying in the US for peace of mind (warranty, loss/theft protection) etc.
If you do indeed choose to buy in HK, then either visit one of the more established jewelers such as TSL or Chow Sang Sang but my recommendation would be to visit an indian jeweler in the basement of the Holiday Inn Golden Mile - Paras Jaims - my family has been buying from them for several decades and have never had an issue.