it seems theres a used watch store on every corner in kowloon. tiny hole in the wall places with no security. lots of vintage rolex watches. when i was there in 2011 i could of had a 5513 for $3500 U.S. that was the asking price. keep in mind a lot of the watches there are fixed for sale, and the 5513 i looked at had end links from a 14060. who knows what else it was pieced together with. i would definitely ask to see the inside of the case when buying in hong kong. I remember seeing lots of modern subs on the second hand market in kowloon wrapped in cling film and piled in the store window, all genuine, tossed aside with little care.
I hear Germany has good prices for certain Rolex models and Japan is supposed to have the best prices on used Omegas.