A typical wall outlet can only draw 1800w (1.8kw) no way is it drawing 40kwh (kw/h is a nonsense unit in this context). If it's drawing 40wh ghats actually quite low, a typical monitor is closer to 80-100w while powered on.

Where I live electricity is about 10c/kwh (cheap I know) so a 100w monitor is costing me about a cent an hour. More than worth it imo but you make your own decisions.