Sorry i thought i added the link. I've got a sample on the way.
http://www.bevelmounts.com/bevelmounts_010.htm
So for an a3 prints packed ready for retail will cost me £2.35 which sound pretty awesome price broken down below.
DSC labs a3 print = £1.10
Standard mount 508mm x 406mm = £0.75
Poly bag 508mm x 406mm = £0.20
Backing Board 508mm x 406mm = £0.30