My answer would be no. Quite frankly I am surprised that you son would request that of you.
The fact that his intended comes from a wealthy family is not, in my view, a reason.
So, my answer would be no with some advice to cut back on the number of guests, change the venue, whatever. I would also want to know how many of those guests are on the brides side and how many, if any, are there for business reasons rather that personal reasons.
But, I am someone who does not always follow the group thought. I tend to be a bit of an independent thinker much to my spouse's disdain at times.
Once you say yes to this request you are also leaving yourself open to any of the inevitable cost overruns which may occur.
I am not saying do not participate in the funding. What I am saying is participate at the level that you are comfortable with...financially and otherwise. And make it crystal clear that the number is is number.
We spent $8K on our daughters wedding nine years ago. No gift at that time.
We recently gave them a six figure check as wedding gift. At a time when the money counted and was used in a productive manner rather that frittered away.
Never mind all that silly pressure to match the opposite family or participate in a way that you do not agree with. Just do what you think is right and what is reasonable.
Besides...how will you feel if they split up in three years? Money down the drain.