Would a Tesco bag suffice? They are free and would do the same job].
LOL, I do, but I splurge on the Tesco 10p 'green' bags, they are the perfect size for a 35cm Kelly, they fold up to nothing and weigh nothing so it's always in my Kelly just in case of rain.
I use the Pliage for travel when I have to push Kelly or Bolide under the seat and for travelling in less salubrious areas, when I want to keep a low bag profile.
LOL, have bought 2 bags for my Kelly (they double up for my Bolide too) One is the pliage, and then for the inside of Kelly, a VIP bag insert oh and another present for my bag, a 'purse hook' from so-hooked.com!
My H bags are spoiled rotten, lol.
When you go to Paris, the Longchamp store is just a couple of blocks away from FSH.