its chinese tradition and estimate how much is it worth for the dinner, where it is held, etc... for a decent family, it should cost them around RM1k per table, if 10 people allocated to a table then RM100 each... so if 2 of you go then RM200 lor... you will still get people who doesn't pay or pay less, this will be written down in their list, even worse if you give ang pow without name on it, as this will be taken as someone did not pay, the nameless ang pow will be classified as bonus... becareful of karma, what goes around comes around.

well then just go with what you think it's worth while... if you don't go then an ang pow in return as a token appreciation on invitation won't hurt good luck