If you are going in March and don't already have reservations it might be difficult for you to get one at this point. If you do already have reservations and the Disney site let you make them it *should* be open before your trip. For dinner, in March (which is peak due to spring break) I would expect at least $70 for an adult, $40-50 for a child.
Another option you might have more luck getting a reservation with and is less expensive is Akershus in Epcot. You do see Cinderella, though she isn't the princess you get the Photopass picture with (Belle is).