I thought carefully about your statement and did a few calculations.
I'm currently using a 17" CRT, with a consumption of 90W. I've found a 19" LCD with a consumption of 18W. That's five times less (better than you said, in fact), but costs 150€.
Given that electricity costs a mean of 0.15€/kWh and that I use my home computer around 5 hours per day, I would save 5*(90-18)/1000 kWh per day, that is, 0.054€ per day.
To get to the 150€ the LCD display would cost me, I'll need 2777.8 days, that is, more than seven years and half.
That said, I'm gonna stick with my CRT until it dies, since I'd rather have the 150€ spent on something else than wait 7 years to get them back.