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
@mozartfan  I have a tube amp and it is a wonderful performer. I also have a class A amp and it is also blissful. My latest DAC - the Schiit Modius - is not a tube product, but it is transparent and the overall sound quality of my system is beyond anything I thought I would ever own. I may play with another DAC in the near future and I have looked at tube DACs, with a couple landing in my price range: the Black Ice products and the Musical Paradise products come to mind. Actually, the $499 model MP DAC is under redesign and will not be available until year-end, so that's not an option, right now.

Frankly, I have been blown away at every purchase from Schiit. I never dreamed their $799 Aegir would match so well with my Moabs. For people with lower a lower budget, companies like Schiit are a Godsend. 
" TUBE Digital is far superior to any DAC "
The tubes in your Shanling cd player aren't going to produce anything without the DAC that's in it
I think this is an issue of definition, with @mozartfan seeming to differentiate between a straight DAC and a DAC that includes a tube stage?