I'm flighting international with a few suitcases and want to buy a domestic flight on arrival day. Obviously this domestic flight will not respect my international allowance. I know Chinese law states excess baggage is 1.5% of a Y ticket per KG. As I will be about 30KG over I was wondering what is the best and cheapest way to handle the excess baggage?

The domestic airline will be China Southern.

I have enough time to post the suitcase if anyone will do it cheaper and I'm not in a rush to receive it.