I've been to Gettysburg. Now I'm putting Antietam on "places to see" this fall. I think that would be the perfect time to go. Not in sweltering heat like now.
I'm sure they have a hotel where I can crash and make a weekend out of it.
Across the Potomac River from Sharpsburg, MD (the town where "Antietam" was fought), is Shepherdstown, WV, where I've found prices to be lower.
Map:
https://goo.gl/maps/yoyTPfYGBeD2The Bavarian Inn would be nice for a vacation, perhaps, but it's pricey and I go cheap if I'm just sleeping there and spending my time at the battlefield. But if you can splurge on a meal, I'd recommend it (I like the Rathskeller dining room).
As for the battlefield, it's set up nicely to go north to south, just as the phases of the battle went. Just don't short yourself on the end of the day, as Burnside's Bridge is a must-see (and I'm not just saying that because I have great memories of learning to waltz there! ^-^).
If you have planned enough time and want a little hike, do the loop by Burnside's Bridge that takes you to Snavely's Ford --where the Union could have crossed the creek, but instead repeatedly bunched up and marched over a narrow bridge under the barrels of sharpshooters dug in across the way -- it's a nice walk through the woods along Antietam Creek. Just PLEASE remember to coat up with a high enough concentration of DEET!
The Sharpsburg battlefield is, at the same time, a place of great beauty and one for deep contemplation.