What to wear to a Vintage Ballroom party?

I have been invited to an exclusive vintage ballroom party, an event where theme dress is encouraged. I am so excited to attend, but have no idea what to wear (and don't want to spend any money). I did an image search to try to get some ideas, but all that comes up are dresses for ballroom dancing competitions and prom dresses. What is even more confusing is that the logo for the party has a picture of a girl dressed as a flapper.

I think I might have an idea about what I am going to wear...now I just have to find some shoes. Oy vey!