The graphics card is ~20-30W IIRC.

But at idle the monitor's powered down anyway, so surely if the
comparison is to determine the significance of the monitor's
consumption, then we need to look at consumotion with the PC
running and outputting graphics?

Say it breaks down like this:
CPU: 70W
Graphics: 30W
Motherboard: 10W
All other cards: 5W
2x hard drives: 30W
Losses in PSU: 30W
(there's a very good reason it has it's own fan!)
2x case fans, cpu fan: 10W

Total: 185W

--
Grunff

This is possibly peak requirements?

The case fans must be pretty hefty to be sucking that much power...
I have an 80mm one in fromt of me, it's only 0.14A (1.68w)

The most reliable way to see would be to actually measure it!

Sparks...