It all depends on your background too - In Indian weddings it's customary to invite everyone and their brother. As a result, the community goes to weddings for the kids of people they know, not that they know them themselves. It's kinda ****ed, it's changing with out generation (I won't go if I don't know them - I couldn't give a shit...).
That being said, my wedding in vancouver had 600 people. Let me tell you, with an Indian wedding, buffet style (which most are) we are WELL below $100 per head... We had a family of 6 show up with $21 gift (we do $1 extra as we deem it lucky, so $101, $201, etc)
If it's my parents forcing me to go, we'll go $50-$100 for the two of us. If it's friends, it's $200 from the 2 of us. If it's non Indian friends wedding, between $250 and $300 depending.
2007 Z4 3.0si