As other posters have said, fabric is really expensive in Europe and we pay around $22-$24 a metre (39" as opposed to a 36" yard). We import almost all our fabrics from y'all and I buy mostly from the US. You do find a line specifically made for the UK and European market now and again, but they probably turn up on internet web sites.
Coupled with that, Paris is itself an expensive city................ If you haven't been before you'll find it eye-wateringly so.
There's a lot to see in Paris and if you're going to give up valuable sight-seeing time, I think you'd have quite a bit of fun if you went to the huge flea market Marché aux Puces de St-Ouen (reputed to be the largest in the world) or Les Puces de Montreuil. These are on at the weekend. There are also other markets on other days and will certainly give you an authentic taste of Paris. Be prepared to haggle.
Enjoy your trip!