You can buy a Canon 70-300 IS USM lens at £269.00 (2,479.67 RMB) via Hong Kong postage free from an established eBay vendor. You would need an eBay and PayPal accounts both registered to your address in China. You risk getting clobbered 20% import duty by Chinese Customs. I got caught when I had a cheap rubbish camera that was included as a sales incentive gift on a piece of second hand software. They calculate the duty on the full cost of the consignment including carriage and tax paid outside of China. You would probably have issues trying to get a warranty as the standard warranty (not included in the price) is aimed at UK customers. Either way, you would still have to return a faulty lens back to Hong Kong. Or you could fly to Hong Kong but finding a supplier with wholesale prices could be more difficult.
The best price I could negotiate for the same lens from Computer City on Renmin Nan Lu was 3000 RMB including a one year warranty.
Then there is Taobao where Google Translate never leaves me with a feeling of confidence that the supplier would be there to honour a guarantee always assuming that I can interpret the sales listing in Chinglish.