I love how thorough he always is with his content and producing followups to answer questions. One of the best YouTubers for this type of content right now.
Heat pumps installations are a racket out in the US right now, it's artificial expense to pad out pockets, there is no practical reason it need be that expensive.
Depends on the system, the living space, and the existing HVAC. The box itself can be well under $2k USD, but things like upgrading your ducting can add a lot to the bill if you have a central air system.