Make-up Make-up Make-up!
Instead of masks, get someone who can do makeup...
clown makeup is not too hard, and if you mess it up, that is what you need, crazy evil looking clown makeup!
Do a search on google images for evil clown, like penny wise and captain shiner to get exmaples of how to do the makeup.
A clown mask is scary for a brief time, good evil clown makeup will stick with them for life. <evil clown cackle>