Q: What are the average of prices and what brands are there?
You'll find the best brands at La Vallée Village http://www.lavalleevillage.com/ it's in The outskirts of Paris, train RER A (you can take it at La Defense), articles are cheaper than if you buy them in Paris but not really given.
The cheapest is not in Paris but in the city of Troyes, 1:25' from Paris by train from Gare de l'Est. Good brands and great prices.
There's also Usines Center in the outskirts of Paris at Velizy but they don't sell the best brands.