I was hoping to keep the costs down.
catch22, I have used the P&G speed controller for an application, and like you was faced with
very little manufacturer's support or searchable documentation, but with a volt meter I was able
to measure the values on the wires for the joystick(while under normal power on conditions), it
turned out to only need two analog voltages, one for speed and one for direction.
these two analog voltages ranged between 1Vdc(max speed reverse) to 4Vdc(max speed forwards)
and 2.5Vdc as motor stopped, if the analog voltage went under 1Vdc or over 4Vdc the speed controller
would go into a fault mode(disabling the drive), also if the controller was turned on without both analog
voltages at 2.5Vdc the controller would fault out. these safety features plus the controllers plug & play
electric motor brake control makes it an attractive option(until the controller has a problem).
to keep costs down you should be able to get by with a sabertooth 2x25 as a speed controller.