We are going to Florida via AutoTrain in August. My daughter goes to college in Orlando and we are taking her car down, staying at Disney, then she'll go off to college my younger D and I will fly home (leaving hubby home to work, this trip).
We rented 2 roomettes (the 3 of us). If was cheaper than 1 bedroom. We also got in on the $19 kids fare. The total for 2 adults 1 child, 2 roomettes, and an average size car was $609.
You really have to play with the dates and definately book early. I noticed that weekends, including Fridays, were higher than the middle of the week.
We are also planning on traveling down for Christmas. The price going down to Florida the week before Christmas is astronomical. We may opt to drive down as the prices on the return after Christmas but before New Years is more in line with what we are paying this summer, so we may opt to return via autotrain. This August will be the test, we've never taken the autotrain before.