The Pass stuff is expensive because it’s way overbuilt and all parts are hand selected and matched. Other than the capacitors which have ~20 year life span (there are no capacitor that will do better) but are easily replaceable, the amp will work and sound the same as day 1, long after you’re in the ground 
Unlike 99% of products these days, you get what you pay for.
If you’d like the BOM, the amp’s been reverse engineered over on DIY audio and you can build your own for approximately 50% savings. And the actual real designer of the amp is there to help you and give you hints. Not all shall be revealed though because the design is Pass IP. So get ready to do some homework and also, scrounge the world for high quality but no longer produced output devices and hope you don’t end up with fakes.