Estimated Electric Costs

Laptop - 45 watts
Day         .09
Week        .63
Month      2.72
Year    $ 32.66

Desktop and Monitor - 150 watts
Day         .30
Week       2.09
Month      9.07
Year   $ 108.88

Turning off the monitor will greatly reduce the cost.
A monitor takes 90-180 watts.
Your PC (desktop) depend on
CPU
Hard Drive(s)
Memory
Other cards
The size and age of your computer and monitor will effect the cost.
Using energy settings and not just a screensaver will reduce the cost.

Printers
Laser printers take a lot more power.

Also include hubs, routers, speakers, external devices.

Based on .08286 per kWh (residential rate)

Check your hardware, most have plastic or metal tags with ratings.
This would be the maximum that the device would draw.
Watts = Amps times 120 (voltage)
Amps  = Watts divided by 120 (voltage)

So a 20 Amp circuit would handle 2400 watts.
20 times 120 (voltage)
less if the voltage was only 110.
120 volts AC 60Hz

110V x 15A = 1650W
110V x 20A = 2200W
120V x 15A = 1800W
120V x 20A = 2400W