Hi Fran,
I know what you mean about the high postage costs here, I use a courier service which I find cheaper than the PO. The letter get taken to the Uk and posted from there, it is so much cheaper but like you I do try to steer clear of decoupaage. when making cards for my customers I do ask them if they want layered cards or 3d and I do tell them the approx cost of postage I find that this works well and I am never stuck for orders.
Sandra