Are you talking about an AVCS cam gear? Was the $600 an installed price? I'd never pay that much for a single cam gear uninstalled.
I also wouldn't believe $90 to be the correct amount for a new AVCS gear. $90 for an exhaust cam gear sounds about right.
Passenger side intake AVCS cam gear part number is 13320AA01. It lists for $143.43 at www.heubergersubaruparts.com
. I get all my OEM stuff from them because they're in the next state over. You may want to try www.fredbeansparts.com
since you're on the east coast.
Driver side is 13322AA001. It costs the same.
Are you having problems with cam advance? Why are you thinking a cam gear is causing misfires?