They sure look nice. $375 for the set (plus the transmissions) hurts, but I can't exactly remember any mecanum system being particularly cheap. (I inspected 357 at UCF; while I don't remember hard numbers, the casting for their hubs was a large part of their BoM.)
Then again, a pair of AM Shifters will run you $660, plus more in wheels (ones that won't
go Oink! Oink! Boom!); raid your old KoPs for the Kit transmissions, and you can build a Mecanum drive for less than an AM-Shifter-and-6WD setup. (Of course, you'd have to declare the value of those extra two transmissions for your BoM, but I doubt you'll break the $3500 limit.)
This brings about the next question: Who's gonna post video of these things in action first?