I give whatever I'd spend on a gift. So maybe $50 on a friend, more on a close friend, more again on family.

The cost per head IMHO has nothing to do with it. I mean at the end of the day, is the guest supposed to do a rough calculation of the outlay? Google or email places for the meal deal, the price of the bonbonierre, and then check with the bridesmaid whether the orders of service were printed at home or professionally done?

Whatever you'd spend on a gift is fine.

Have fun