I think this is an unanswerable question. You won't save much by doing this and it'll involve a lot of hassle. If you really want to go to multiple shops and barter.
www.taobao.com
OR
The Zhong Guang Cun disctrict in north Beijing. 😉
They got everything you'd ever need....lowest price on a iPhone in Beijing is 3500RMB with receipt 3000RMB for one without a receipt.
But I guess receipts wont do you any good if it's broken anyway ... no service points around.