The delta between economy class prices and first class prices for intra-China flights is nowhere near the delta as we see here in the US. For instance, I just booked a flight on Air China going from Beijing to Shanghai for two weeks from now where the economy fare was $168 and the first class fare was $239. My colleagues in China tell me that that is typical for how the fare structure works.

So I'd encourage you to just check out the first class fare for the flights you are interested in - try it, you just might like it!