craftgrrl | Painting a mural in a bathroom

I have been asked to paint a mural in a little girl’s bathroom of the little mermaid. It ‘s going to be fairly large (about 6ft by 6ft).

It will be painted above a large whirlpool-ish bathtub like the really big nice ones (not for sure what they are called). My question is what kind of paint would you ladies suggest using I didn’t know if acrylic would be the best thing to use since there would be the problem of steam and such since after all it is a bathroom.
I like working with acrylics, but didn’t know is there was something else more suitable.
Also how much would one charge for this? I’ve only ever done painting for my local movie theater and they only gave me free movie passes. I don’t want to over charge and then again don’t want to sale myself short.
Thank you, any help is much appreciated!