I'm a Fluval dealer and I pay more at wholesale for the FX5 than the ebay sellers sell them for, and they include shipping. They honestly cant be making more than a few dollars if that.
I use the FX5 on my tanks, and i think its an absolutely fantastic filter.
^^ mine is loaded to the hilt with ceramic media in every spot of each tray except for the center of the top tray which I use ac110 foams I cut to fit. For further mechanical filtration I just use a magnum H.O.B. as needed.