There have been numerous suggestions including one that Fiat has designed for the 124. They are in the forum. I just did a forum search for "luggage" and found nearly a dozen postings.
This is the same one that was on the car at the Paris Auto Show.
People like luggage racks for the looks, few will actually use it for luggage.You can try taking out the trunk side liners for more space. There's actually quite a bit of space hidden behind those liners, but you gotta be careful of the cables.
This one is indeed cheaper, and easy to install/remove, but the look is not so nice,This one is a bit cheaper, attaches via vacuum suction cups...http://www.ebay.co.uk/itm/182361462730