It seems I have found a solution. The costs would be as follows:
The total of €30.55 would be shared amongst all of us, i.e. around €2.50 each with 12 of us. The onward postage from London to each recipient would be on top of this. Ubidoca seem a lot more accommodating than French Office.
If you're interested and I don't already have your e-mail address, please PM me.