Dear
Due to the price increase in the raw material, we also have to unluckily raise the cost of our merchandise to you.
We have tried our best to avoid raising our prices for as long as we could, but we can no longer continue with the same prices. We have enclosed our new catalog with the new price list for your review which goes into effect on (date). Although, all orders placed between now and (date of increase in prices) will be honored at the earlier prices only.
We wish to thank you for being our valued customer and I know that you will understand the necessity for this price increase.