My eyes nearly popped out of my head.
I was looking for solutions to connecting more than one MPPT to a MultiPlus II GX and thought, "Could I use a VE.Can port with a VE.Direct to VE.Can adapter?".
Sure enough, there is such a thing "VE.Direct to VE.Can interface" (ASS030520410) but it is about the same price as the MPPT I want to connect about 300EUR.
Now, I have since learned that you cannot use VE.Can on the MultiPlus II GX for MPPTs but I am still interested in why the VE.Direct to VE.Can interface is so expensive?