(Picking my jaw up off the floor....)
Obviously, where you live makes a HUGE difference!
If it's an acquaintance, I usually give in the $20 range. A close friend might go up to $50. Probably the most I've ever given was to my siblings....they get in the $200-300 range, but that's VERY generous for this area. Also, I never give cash at weddings, but give gifts.