Hi Misty!
The Dining Plan is based on options and length of stay. You generally won't know the cost until you get into booking your vacation, either via online or through a booking agent.
In terms of dining plan, for 2 adults with no children, I recommend the Standard or Basic Dining Plan. This plans give you a little of everything: 1 table service meal, 1 quick service meal, and 1 snack per day. The Deluxe is a great plan, but a ton of eating! If you're not bringing any children, and not looking to secure a ton of character meals, the Deluxe is probably not for you.
The Quick Service is good, but I always feel it's nice to be treated at least once or twice with a serviced meal. Plus, table service meals are more of the cuisine variety, and, you can look secure character meals or even Signature dishes if you desire under the Standard Dining Plan.
Good luck and best wishes and your Disney trip!