Graduation Gift

Our neighbor, (who we've been with twice,) but enjoy talking to when we're outdoors, sent us a graduation invite for their son's graduation party. We don't know him at all, and he very seldom speaks to us. Should we take him a gift of money? If so, how much is appropriate? The family is quite wealthy, so I don't think they did it for that reason. It may be something he is looking forward too!!
Thank you