I've had up-dos for formal night. For any hair stylist services on formal night, be sure to make your appointment as soon as you board. The formal nights, especially right before dinner, are very busy so early scheduling is a must.
I don't recall the costs, as it's been a few years. They may be listed on the Carnival site. But they will often try to sell you a barette or other adornment, which can easily add on another $25 or so. Last couple of times, I brought my own.