CorpJuris,
Welcome to the site. It really depends on how much you want to spend really. The expensive Givi's go for a few hundred dollars, but they are very good quality, and the cheaper ones, which I have on mine, are only about $60. Mine is a Bestem and it isn't the quality of Givi but I have had it for almost 5 years now and it is still in pretty good shape.
Search ebay for some of the cheaper ones but make sure it comes with the rack that is needed.
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Ride Safe,
JeffR_
Givi Airflow, Dr Pulley Sliders (28gr), Power Commander, Air Hawk, K&N Filter
2007 Silver Wing 34,000 miles
2005 Majesty (sold) 12,500 miles
2004 Reflex (sold) 3,500 miles