It's been a couple of years since I was in Paris, but the Kookai chain used to be considered moderate and very branché. Also you might try the Prisunic and Monoprix (think Target but owned by the Galeries Lafayette and Printemps) stores-and they have big branches on the Champs d'Elysee. Finally a number of designers have outlets on Rue Alesia.

Hope that helps, P.Miller N. Fla