I know a lot of the Asian caterers for weddings in Adelaide and Sydney - you start seeing the same ones and talking to the same ppl when you shoot them long enough, and it is around $80 to $120 ish roughly per head for an 8 to 10 course meal - this is a very loose figure btw as it really depends on what specialty the client orders too. But Asian etiquette here in Aus, or in VN or China or Malaysia or Cambodia and other places that I have attended - it is generally give at least the same amount that it costed for your catering plus a little bit more on top for good luck and present etc.
Worse family I had seen gave 40 or 50 bucks altogether and rocked up as a family of 4.....needless to say in the ante room where we prepare our gear and the bridal party counts the money - a lot of nasty things were mentioned about the aforesaid family.....