Not at any price.

This phrase originated around the late 19th/early 20th centuries and derives from the fact that China was well-known to produce tea in huge quantities. That's still the case and China now accounts for around a quarter of the world's production of tea. So, to decline the offer to do something 'for all the tea in China' is to be determined not to do it, whatever inducement is offered.

The Oxford English Dictionary declares the phrase to be of Australian origin and reprints Eric Partridge's 1890s date for the phrase, but unfortunately doesn't provide any supporting evidence for either assertion. The nearest I can come to verifying the date, and to an Australian origin, is J. J. Mann's travelogue Round the world in a motor car, 1914:

AUSTRALIA is not a hospitable country for anybody that has not got a white skin, and a clear record of white skins. By the laws of the country no dusky, tawny, or yellow races are allowed to land... When the question came up of letting in our Indian fellow subjects, an education standard was established, and if the unlucky Indian does not happen to know all the languages of Europe he is floored in his examination, and must stay outside. One is not even allowed to bring in a black servant, and when I applied to the authorities for permission to bring Samand with me, the reply was : "Not for all the tea in China."