I don't know if this is the most accurate way of calculating this, but here's what I do. Work out what percentage of the total house is your salon. Say your salon takes up 20% of the total house area, then I'd add an extra ten percent to this - my reasoning for this is that the salon probably uses more electricity/phone calls than the average house due to wax pots, airconditioning, etc being on all day. You probably do a lot more washing for the salon than the house too.
Anyway working off those figures, the salon uses 30% of the household total so you should be able to figure out an estimate based on that.
Hopefully someone else comes along with a much better idea than this, like I said it's probably not the best way to work this out but that's the only way I could think of when calculating my costs.