That is 3KW. Check your electricity bill and you will how much they charge you for 1KW. Multiply that by 3 and add 5% VAT - that will be the maximum cost per hour
I'm guessing you're just looking for approximate figures.
It's a 3KW heater so, if you look at how much /KWH you electricity costs in p/hour and multiply by 3 that will give you a rough cost for running it as a heater - probably around 45p/hour.
As a cooling fan it will probably be about 40watt, so less than 1p /hour.