I have bought several large carpets at the Brocki in St. Gallen. It is a second hand store, but the Brocki in St. Gallen sells the left over carpet that people have dropped off and the carpet is brand new and sells anywhere from
25 CHF-50 CHF. It's nice Berber carpet and comes in all different colors. I have never checked out a Brocki in the Basel region, but below are 2 sites where you can find Brocki's. They might also have carpets or rugs. If not, then it might be worth the drive to St. Gallen. Hope this helps and good luck!
http://market.local.ch/de/m/secondhandshops/BL www.brocki.ch