Cost of turning monitors off vs. leaving in sleep mode

[Lottery Larry]

I'm trying to determine the approximate cost of leaving on your computer monitor overnight (in power-saving sleep mode) versus turning it off at night and on when you need it.
This is to settle a bet, so it's important :P

A few studies I've googled seem to suggest a $20 annual? power savings for CRT monitors, which consume about 3-5 watts/hour, if I'm translating the studies properly

Anyone have a reference source that I can point my opponent to, to validate an approximate number? I need to calculate an approximate cost/hour value, rather than an annual cost.

If $20/annum is pretty close, then I lose.

Thanks for any help.