is the cheapest meal (relatively) followed by lunch and then dinner. Our upcoming lunch for two adults, one Disney adult (11 years old) and one child will cost $210.58 which includes the picture package, tax and gratuity. This is in June when Disney typically charges a few dollars extra for CRT and some other places. So we are probably paying something like $56 for adults and $32 for a child. That's a rough estimate. The total is precise.
If you have the dining plan already set up, note that when you make your ADR. They should still take your CC number but not charge it unless you are a no show.
In some cases people make an ADR prior to having their package booked. In that case you can call back when you have your package reserved. Disney should refund your credit card charge. I do not know the turn around time for the refund. The initial charge will happen almost immediately after you have booked.