Hi,
We have used AutoTrain twice and plan to use it this December for our upcoming trip. If you're not to keen on flying and/or want a peacful way to get to FL, the AutoTrain is a GREAT alternative. You can pack as much as you want in your car and not have to worry about (or pay) for a rental car. Other than AAA, there are very few discounts for the AutoTrain. They do sometimes run specials for it, but they are announced only a few months before travel dates. I believe Amtrak will allow you to change your fare, if you were to purchase at a higher fare and the fare goes down. There may be a small fee to change it, but they would refund your money. That is what the agent told me when I inquired.
The AutoTrain fare includes a good dinner and continental breakfast on the train as well as transport of your car.
If you do a search on this board, you'll find lots of info on the AutoTrain.
If you have any other questions, please feel free to ask...