The easiest way is to use old band uniforms. If you are at a school you could use theirs or contact a local band uniform rep and they sometimes have old samples they will donate or sell cheap. You mave have to remove or cover schools names but it will give you a great look. You could also approach a local tux rental place and see if they will give you Tails at a resonable rate. You can go the tunic and tights route as well which can be easily made.