I am not based in Shenzhen but have been mostly based in China for 15 years. Some general comments only. Usually cable is purchased in bulk here. Electronics markets in any city will custom-rig cables in your selection of quality (usually across multiple manufacturers), color and length for peanuts. Pre-fab cables from a factory always cost significantly more if you order them individually wrapped, though they can be better quality (though my experience here is mostly ethernet but I had custom-run fiber to premises in a second-tier city as early as 9 years ago / 2007). Fiber is everywhere today in China, the equipment for splicing is widespread and cheap. Patch panels and other primarily metal components are cheap, though you want to check quality before buying in bulk, then find a factory and order direct and in quantity emphasizing future volume expectations. Of course, if you are here you can check quality immediately, if you want to do it remotely you are looking at shipping delays x2. If you just want a quick price delta, go to taobao.com, translate your part name, then get dealer/distributor pricing for consumer or business small-scale China domestic purchasing, usually inc. shipping.