A wedding is one occasion that requires you to be both on theme and in season, which is why you don't want to be caught scrambling at the very last minute. To ensure you're ready for your next set of nuptials, we found some wow-worthy fall cocktail dresses that - ahem - are all available on Amazon for under $50. Hey, if you're buying a new outfit for a wedding on top of giving a gift, it doesn't hurt to be budget-conscious. By definition, cocktail attire means that your look leans toward the formal side, so your wedding guest dress should be mini, knee- or midi-length.