There are two places to eat breakfast at RPH. The more expensive option is at the Islands Dining Room. It is a big buffet for around $20/person. The other option is the continental style buffet in the lounge which allows you to buy individual items like bagels, croissants, juice, cereal, etc.
There are also other options. Pastamore in Citywalk has reasonable breakfast items including a breakfast pizza. IOA has Croissant Moon and Cinnabon and Universal has Boulangerie which has excellent egg, cheese and bacon/ham croissants.