A buddy box is just a slave, so it can be anything cheap. The box actually controlling the pane is your brand new Futaba 2.4
The trick is the cord that connects both boxes. Futaba recently changed it so you need to make sure that the cord can connect both boxes.
I have a Spektrum Dx6i, I bought another Spektrum Dx5 w a broken antenna for $15 at flee bay and it worked wonderful. Both were Spektrum so the cord fitted well.