When I used to live in Georgia, I often took The Crescent from Atlanta to New Orleans, and upgraded my coach ticket to roomette. This was just a few years ago (2008), but I remember the coach ticket was $58, and the accommodation charge for the roomette was $47. This was the "V4" level, which was the least expensive. The previous contributor was correct in that the price increases due to availability. Be sure to ask your reservations agent about this, in order to get the best price. It helps greatly if you're flexible on dates.
Assuming you are a First Class passenger, you will board at the Atlanta station at about 8:30. Once the conductor accounts for you by taking your ticket, you will be called to the diner for breakfast. My usual is the Omelette, with a side of sausage, juice and coffee.
Around noontime, you will be called (first, before coach passengers) to lunch. I usually order the chef's special, tea and dessert.
Then, just before you cross into Louisiana, there will be one (only one) dinner call. My choice has consistently been the flat iron steak, baked potato, vegetable of the day, tea and dessert.
Since I only travelled single, I'm not sure how the meal arrangements would be handled for two. I presume that each would pay for the coach seat, then the roomette upgrade would be charged once (since there are two seats and an upper and lower berth). But it seems that meals for two would be a loss for Amtrak, and Amtrak doesn't seem to be in business to lose money (at least that's my observation as a passenger).
-Robert