Ballroom Dancers

Ok, I thought about it and decided that only the actual ballroom dancers need a "ball gown". The rest of the cast can wear the same costume throughout the entire play. So here are some idea's for a ball gown.

This is an example of a Renaissance Faire costume

If you would like to sew your own this is a current simplicity pattern. 

The easiest option is to try to find something like this at a thrift store.
Then add sleeve or put a long sleeved blouse underneath. No modern colors please.