I would look on Ebay once you know what you are after. I got brand new set for thenew 4x4 for £106 all in, (genuine Fiat parts) which is a substantial saving on the cheapest dealer price. The cars without roof rails already fitted use a different type of bars that are cheaper to buy, or you need to pay out 170 or so for the roof rails as well. These can be had in a range of bright colours at this price new. SOme good offers on this on ebay from time to time.
A decent set of second hand roof bars in really good condition for the Pop Panda seem to sell for £50-60. Happy hunting.