The bustier is a popular type of lingerie, in some ways similar to a bra and in other ways similar to a corset. It creates cleavage and usually also reduces waist size. There are strapless styles, and also styles with straps.
The major difference from a bra is that the fabric extends much further down the body, below the chest. The major difference from a corset is that it's much less constricting. The preponderance of women wearing corsets ended around 1920, in part because of the introduction of the bustier.
Commonly available bustiers sell in a price range from roughly $15 to $200 -- prices around $50 are very frequent. Prices can also be much higher in some cases, such as bustiers made of exotic materials, or ones with embedded jewels.