I mainly agree with Martin on this one, whilst its true, that an awful lot of clients or prospects will try to compare quotes on an hourly basis, you should not fall into this trap.
You need to explain to the client all costs associated with their cleaning, insurance/training/equipment and chemicals etc. Once these costs have been factored in, so to speak, your "hourly charge" will be quite high, you need to have the ability and confidence to convince your client or prospect, that your own costs to provide an excellent service cover more than just the cleaners time on-site, a low hourly charge, will quite frequently mean, a poorly run business, where important details and obligations are not met, this is your opportunity to educate your client or prospect on the realities of life, regards,
Rob