The number one question to ask is, ‘Will I ever be wearing this ball dress again?’ If the answer is no, then there is truly no point in spending an extraordinary amount of money on it. Today, fashion is incredibly fast-paced, with high volumes of dresses on a variety of websites for affordable prices. Check out the online high street stores which usually have a debs/prom section on their website. Try the usual: Boohoo, Pretty Little Thing, Missguided, or Asos.
Set yourself a limit on price. The ball outing can be an expensive night, so do not forget that. Between the ticket, drinks, taxi, etc. it all adds up. If you are planning on buying matching or coordinating shoes, set a budget for yourself there, too.
Ask your friends for a loan of their old debs dress or one they have worn to a previous ball. Maybe change the accessories? It is up to you. You can always find a bargain in a charity or vintage shop. It does not have to be perfect – you can always go to a seamstress and have it adjusted to your preference.
On a similar train of thought, why not transform a dress you already own? Bring it to a seamstress/dressmaker and ask their opinion on what changes could be made!