What makes a DAC so expensive?


You can buy a Cambridge Audio AXA25 25 Watt 2-Channel Integrated Stereo Amplifier | 3.5mm Input, USB Input for $225, and most DACs seem more costly. 

I'm wondering what it is that makes a Bifrost 2 almost as expensive as an Aegir and 3x's as expensive as the Cambridge product, above. I would have thought an Aegir would out-expense a Bifrost by a factor of two or three. What are the parts that make the difference? 

I'm wondering if the isolated DAC concept is one that comes with a "luxury" tax affixed. Can anyone explain what I'm getting in a Bifrost 2, or other similar product that justifies the expense...?

Thank you.
listening99
If the DAC is reconstructing the waveform optimally and the measurements for distortion and noise shows they are not audible that’s correct it doesn’t have a sound signature, it’s a well engineered transparent DAC. I understand not all DACs are transparent.  
What I'm seeking to clarify is how "Power supply noise and OP amp compression" influence THD + N?

What measurements meaningfully capture power supply noise and OP amp compression?
A:  My friend just died of a stroke

B:  But his body temp was exactly 98.6 - he was healthy

A:  He smoked like a chimney and ate bacon every meal

B:  But his blood pressure was exactly at the mid point of normal range for his age and weight

A:  Are you an idiot - he is dead

B:  I believe based on my measurements he is still alive

A:  Dumb ass

Power supply noise will show when THD+N is measured. There could be a lousy power supply which would be audible. All DACs will have noise from a power supply but do they effectively deal with it. If a DAC is audibly transparent , distortion and noise is below the threshold of human hearing, I'm not sure I understand the point. 
No audio equipment is 100% transparent to the human ear, not the recording studio equipment, and not the playback equipment.