The are 6 different ways across 3 unique modes of transportation to help you travel from Atlanta to Montgomery. If you're only considering the price, you should check out the bus out of Atlanta towards Montgomery, as it is the cheapest to Montgomery. It's common to find tickets for as low as $14. Greyhound operates from Atlanta to Montgomery, so you book your trip with them! Book as soon as you can, as there may be limited availability.
On your trip from Atlanta to Montgomery, it is best to book as soon as possible. It won't necessarily help reduce your price by a large amount, but will ensure that you have a spot on the bus or train.