Dealing with odd requests

Just wondering how you guys deal with odd requests. I had a woman call wanting me to paint her four kids Halloween morning and I just don't event know how to quote these. I told her if she was willing to come to me, we could work out a fair price. She absolutely wants to pay, but I just don't know what to charge or really want to honestly.

On Halloween I charge $25/adult and $10/children to be face painted at my home studio. I set-up appointments...

For SFX I charge more of course depending on what they want.

It is all done at my location.

I wish I had thought of that to put up a sign to this effect at the festival I did this weekend. The call I got was from it. I would have probably had lots of requests. You live and you learn I guess!