If you are on a tight budget, your best bet is this Alice + Olivia Romper. It's a fantastic piece, while not very pricey. In this price range, you can also take a look at this Jumpsuit. It's also a popular item and won't break the bank.
If you're looking for a bargain, look no further than this Kenzo Romper. This item doesn't cost the earth, but absolutely invaluable in your wardrobe.