Agreed. Rimage charges a huge markup on their drives.
One thing that you have to be careful of if you go with your own drive is the extension of the tray. Drives made for use in autoloaders extend out a bit further than normal to work properly with the robotics. I think this is something that can be controlled via firmware, but I'm not positive.
You might try asking your Rimage VAR about this. There are a couple guys at the company I use for service and sales that know the in's and out's of this stuff and they have helped me with all of my upgrades.