Beit Din Tomorrow!

Hey guys, any advice? My Rabbi kind of sprung this on me last minute and I'm a little bit freaking out. My mikvah is tomorrow and told me to prepare a note of thanks and a gift for the members of the beit din and my mikvah attendant and also to contact the mikvah about how much an acceptable donation is to use it x.x

It's Sunday so they aren't returning my calls. And as far as the gifts go, I am thinking a nice note and a donation to their discretionary funds would be appropriate? Do I include the amount donated in their card? I was cool as a cucumber until I found out about all of this TODAY. Pls help