There's something to be said for regulated cooling. Whether that's worth the $$$ over a used Nikon is up to the buyer
This is not intended as defence for ZWO - I have no connection to them besides owning one of their cameras - but buying those sensors and developing a camera around them, especially in limited numbers, has a cost. Who knows what the wholesale cost of those sensors is, in such small quantities. Just putting a scenario out there that doesn't entirely centre on price gouging...