Cost of Electric?

Hi all

have seen many different costs for electric for running HPS. but i saw this on ebay, form the people selling envirolite grow blubs

125w ENVIROLITE 6400K Grow Lamp + Single Reflector New - eBay Plants Seeds Bulbs, Garden Plants, Home Garden (end time 08-Nov-07 23:46:07 GMT)

on that page they state the following as cost of electric per WEEK.

400w hps £9.37
600w hps £14.04
1000w hps £23.40

This is the highest I have seem . is this right. if i run one 1000w is it going to cost me about £100 a month???????

figure out how much you pay per kwh for electric than do some math a 400w= .4 kwh 600=.6 1000=1 so1 x 12 hours =12x 30days in a month=360xprice per kwh i think thats the formula it would costt me like $25us per mounth to run a 1000w