Pricing for a non-profit event, how do you estimate? Thanks!!

When you face paint for a non-profit event, how do you decide what to charge, etc.
Thanks so much!

I have never done any corporate events or festivals/fairs so I don't even know how to begin.

Regular hourly rate.

If they book 4 hours I charge them for 3.25 hours - that's the only discount I offer to non-profits that I am willing to support. I don't offer it to all that ask.

I used to offer a way larger discount, but decided I still worked just as hard or harder... so, this is it now.

I used to give a bigger discount, but my calendar was filling up with so many of them that I wasn't able to book any full rate events. Now it is either 30% off of my hourly rate or I do PPF with 30% going to the charity if they have no budget for it. If neither of those works for them, I will sometimes donate a GC to their auction or prizes.

I usually do only one or two a yr and keep a small amount for my time and paint used. Relay For Life is the one I do every year.

If I did more charity events, then I'd do a percentage. I feel like I'm giving back and that's what it's all about

I discount 10% off from my hourly rate.

Tanks so much for your input, I was contacted by St. Jude Hospital to paint for their walk, I have no idea how long will I be painting for, I have been to the LLS walk and I remember being there for at least 5 hours if not more, not sure about St. Jude's though.
It is hard to put a price because this is a charity dear to heart. I was thinking of just making enough to cover paints and time. Maybe I'll do my hourly rate and then donate part of it.
Oh, what a pickle.

I charge $5 a face(eye designs to half faces) and then decide at the end how much I give to the charity, but it's usually a good chunk.

For hourly, I offer a 15% discount.

I just wanted to say thank you for all the suggestions, after reading them i was able to email with my prices and guess what??? It looks like I'll be painting for the St. Jude's Walk in November.
So excited about this!!!

Thanks again!