>>> why this third party Amiga hardware is so expensive?

>> what does "third party" actually mean in Amiga context? :-)

> Good question. I used the term to refer to some organization not originally affiliated with
> Commodore/Amiga who produces compatible hardware.

Using this definition, every "Amiga" hardware released since the demise of Commodore has been "third party" :-)
Btw, in the cases of PPC-based hardware, it's not the hardware that is (somewhat) compatible but the OS.