Buy an iPhone, iPad, or iPod in Hong Kong and you will pay no more than the US price - so they are cheaper here because Hong Kong has no sales tax. But try to buy a Nexus 7 and you will pay 20% more, because they are all “parallel imports”.
English books are usually around 25% more than the US price (they usually convert at HK$10 = U$1). Hence the popularity of sites such as Book Depository or Fishpond (though the latter is very confusing, as they have their own made up list prices). Or you can buy your books in Thailand (reasonable prices) or India (very reasonable prices).
There’s also the nonsense of Amazon charging an extra US$2.00 for sending (some) Kindle titles to customers in countries where they don’t operate. Yes, that’s a charge for sending files over the Internet.
Alternative medicines are typically 100% more in Hong Kong. For example, Blackmores Echinacea Forte is sold in Watsons in Hong Kong for around HK$150 whereas in Thailand it is around 600 baht. The catch is that in Hong Kong the pack only contains 30, whereas in Thailand you get 60. So the unit cost is double.
I found another product in Mannings, and went online to check the UK price. Again, it was almost exactly half the Hong Kong price. So I tried to order it online from the manufacturers. They don’t allow you to order from Hong Kong, but instead they direct you to the retailers here who stock their products.
Fortunately there are other companies (such as ChemistDirect) that will ship the same products to Hong Kong, and in many cases the discounts offset the delivery charge, so you are paying the UK retail price with “free” delivery.
Which is about half the price you would pay in Hong Kong.