Venus, the only restaurant that charges is Sabitini's -- the 4 anytime dining restaurants are all free.
We are on the Diamond in October, having done a 2-nighter pre-inaugual on her in March (she is the sister to the Sapphire). The choice of restaurants is fanastic! That's why we booked her in October. You can also order off the tradiitional dining room menue from any of the 4 anytime dining restaurants, so it's the best of both worlds.
I would highly recommend this class of Princess ships.