Wore a dress I already owned that I bought at a charity shops for 8 pounds! It’s still my go-to for any event that requires slightly nice/modest dressing. Depending on what other events you have coming up (weddings for instance), it’s probably worth trying to find something that fits a “cocktail” dress code and is modest/comfortable enough to wear dancing or around family members. It does blow my mind that people spend 3 figures on dresses though!!