You know, the cosplay contest does have - and has always had -- a costume competition part. Entries into cosplay contest are Costume only, skit & costume or Skit only. The costumes and skits are judged separately. Those who choose to do costume only get to walk across the stage (similar to fashion show) to show off their costumes. Usually, the walk-ons go first, then the skits.
It actually takes up far less time than other convention's cosplay competitions. First, we don't lock you in a room all day forcing you to suffer thru all the other entries. You come to an initial meeting, sign up for a time for costume judging (if applicable) & a time for skit technical rehearsal (if applicable) then wander off until shortly before the time(s) you signed up for... then, of course, you will have to go to the green room just prior to the Cosplay event itself to line up in preparation to go on stage.
If you're just doing a skit, then any source of costume is fine.
Requirements for costume judging is that at least 50% is made by you. The point of this is because when judging costumes, we're examining the quality of the construction of the costume based upon the entrant's experience (novice, journeyman, master) and age bracket (youth, minor, adult).