Rose cuts are much cheaper by carat weight. They are also cut very shallow so they will look very large. Because of the way they are cut, they also have a very different appearance - they aren't sparkly. Rose cuts reflect light off the facets rather than sparkle from refraction inside the diamond.
You can't really walk into a store and buy a rose cut - have to go to estate store, vintage stores, etc. Jennifer Aniston's new erring is a rose cut (very over priced and cloudy one).