This is my attempt ...
Dear Customer,
Due to rising costs throughout the last year, we unfortunately have to increase the charge for our services to you.
We have not had to increase our prices since we started our business in April 2007, but unfortunately, the rising cost of fuel and materials, coupled with an increase in the minimum wage and holiday entitlements means we cannot maintain our current price levels any longer.
Your new charge from the next clean will be: £
We wish to thank you for your valued custom and hope that you will understand the need for this price increase. We hope that you feel our service is worth a little extra.
If you have any questions please do not hesitate to contact me.
Yours sincerely,