Impact Guns has the Ruger carbine for $499 (while supplies last). It's listed on Buds at $579. I'm not currently looking to buy one so I haven't shopped around at all for the Ruger, but this seems like a pretty good deal while it lasts.
ruger-pc-carbine-9mm-take-down-16in-barrel-ruger-glock-mags-17rd-mag