It's been a while, but I"ve been on the Grand One three times. We've not actually had "Dinner" but have had appetizers adn desserts catered.
The price has gone up to I think $400 per hour with a two hour minimum, tip additional. Dinner can be served by an onboard butler at an additional charge, or the GF room service can bring it and leave it for you to server yourselves. They do set it up very nicely though--they scattered rose petals around my birthday cake a few years ago.
Let me know if there's anything else you'd like to know.
Anne