A couple of the more expensive styles

The truth is, any style of bathtub can be made more expensive as it depends what the bath is made out of. Materials have different costs which is the main difference in price. However, standardly the free-standing and under-mount bathtubs are usually the most expensive.
Corian is an expensive product and can be used to make a usually cheaper bath like the drop-in instantly more expensive, yet very stylish.
The undermount tub is usally the most expensive. This is mounted under the rim of another material, this is where you see Corian used mostly. However slate, other stones and tiles are also used. They are the least common style, so if you really want to have something different and can afford something this luxurious, then get this one.
If you are happy with your current alcove style bath tub, but simply want to glam it up, then we suggest that you remove the tiles around and replace with something more expensive, you can also change the taps to something more modern and stylish.