See, that is what always interested me. Back in the day it was rare for me to have a single friend visit a gig I was playing, let alone hordes of them. And having a part of my pay go to pay for their drinks was something I wouldn’t even consider doing.
If your friend is a dentist, you don’t go sit in his waiting room all day and expect to be treated for free right?
Organizers and owners don’t mind you bringing “friends” and preferably loads of them, but only if they pay for their drinks. Freebie friends are no good to them.
On-topic: I am not from your neck of the woods, so can’t comment on what a regular fee would be. It would also depend heavily on the gig, duration, type of venue, the following you bring, etx.