Like other commenters I was also confused at the "~$800" comment.
I tried this myself, picking a time a few weeks in the future (round trip April 15th to 22nd). Round trip as I'm assuming you'll want to go there and come home.
All of the following info is for ATL to Washington-Area airports (BWI, DCA, IAD). Amtrak is for Atlanta to Washington Union Station
Delta (20+ nonstop a day every 30min or so, ~2hrs flight time):
- ~$244->$304 Main
- ~$444->$504 Comfort+
- ~$769-$974 First
Amtrak (11:29PM->1:47PM, 14h18m):
- $356 Coach
- $1107 Private Room (Roomette)
I'm sure that a more accurate analysis would include a spread of days.
In general, this means that with the train you'd increase your travel time by ~26 hours round trip (over a whole day) while also paying ~$112 more.
(Note that the Amtrak website prices each leg independently while Delta prices round trip, I made sure to go all the way to the cart to gather the end pricing)
I was curious so I also did a trip much sooner (March 30th to April 6th):
Delta:
- $616-$665 Main
- $785-$800 Comfort Plus
- $1065 First (they were all priced the same)
Amtrak:
- $517 Main
- $1369 Private Room (Roomette)
So for a much sooner trip you do save ~$100 for the tradeoff of ~26 hours more time spent.
It's also worth noting that this route's travel occurs primarily at night, in the dark. This means both trying to sleep on a train as well as not being able to see much outside as it'll be dark most of the ride.