edit, got that wrong: a Rancillo Silva V3 draws 1100 watts, if you have it on for 24hrs a day, that's (1100*24)/1000=26.4KWH per day. So depending on your electricity tariff, a good price is something like 10p/kwh, so it's 26.4*10 = £2.64 per day. I assume however you'd only actually have it on for at most 3 hrs a day (cost £0.33 per day), and even if you did have it on constantly, it's not constantly drawing 1100 watts as the thermostat will cut out the power once that water's hot enough.
Only when the thermostat is switched on. Let it warm up (30 mins+) then calculate the duty cycle. Eg. if it's on 10% of the time then it's actually more like 110 Watts.
edit, got that wrong: a Rancillo Silva V3 draws 1100 watts, if you have it on for 24hrs a day, that's (1100*24)/1000=26.4KWH per day. So depending on your electricity tariff, a good price is something like 10p/kwh, so it's 26.4*10 = £2.64 per day. I assume however you'd only actually have it on for at most 3 hrs a day (cost £0.33 per day), and even if you did have it on constantly, it's not constantly drawing 1100 watts as the thermostat will cut out the power once that water's hot enough.