Not sure how cheap you are looking for but the largest schools in the area are:
Aviaiton Atlanta at PDK (
www.aviationatlanta.com)
ATP at FTY (
www.allatps.com) (US citizens only)
Falcon Acadamy with 5 locations in the area (
www.www.falconaviationacademy.com)
There area also a variety of other flight schools at PDK see the relevent sections here:
PDK - DeKalb Peachtree Airport
Best of luck