Don't think trying to charge them now would be a good way to go. "Horse is out of the barn" Once I started "donating" my services its expected. Try to be a nice guy and you get labeled.
I did suggest that next year I don't do the actual party times of 12-6 but come on afterwards to keep thing going. A lot of people still want to hang out and party and the bar does great. I had trouble quitting at 8:30 last year. The response was that's a great idea but no mention of paying me for it so the only ones making out would be the bartenders and the VFW.
BTW the thing that started me thinking of bailing next year is the fact I found out that the bartenders keep all their tips that day and make out big time. And because its their regular shift day they don't have to buy tickets. They are all volunteeers too but I just feel that everyone invloved should be donating their time that day.