I purchase all my cake boards, fondant etc from fondantsource.com, I get my boxes from webstaurantstore.com
Both sites have good prices and quick shipping.
I will have to check out brpboxshop.com and see what their prices are like. Free shipping would be fantastic.
If you google coupon codes for fondantsource you should be able to find a code to use for 10% off. I have been using the code, welcome, to get 10% off orders.
