Cost per month: $0.19

Cost per month for when:
powered off: $0.27
full running: $23.91
brightness at lowest setting: $16.16
Brightness at highest setting: $21.03
Display is off: $8.24
Computer is sleeping: $0.46

Cost per month for continious charging: $1.66
Cost per month after device is 100% charged: $.10
Cost when nothing is attached to charger: $0