Lavalier mikes - advice please.?

I have a 6-member improv troupe and we need to work towards purchasing a nice set of lavalier mikes. Headsets won't be good because we do use hats, wigs and costumes right on set for quick character changes. Also, we have an audience member come up on stage once or twice during each show. Sometimes a handheld would be okay for them, but sometimes, we have them "act" in a set - like, when we do "Fairy Tale," where an audience member might be, say, the Frog Prince for about 5 minutes. We're on the verge of becoming something special, but right now our budget is still tight. What do you suggest? a href="http://www.dutchblitzkrieg.com" rel="nofollow"http://www.dutchblitzkrieg.com/a