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
As I've said before, the proliferation of costly high-end DACs is a clever marketing ploy to snare the gullible and unwary who conflate performance with price!
A $300 Topping DAC has about the same parts count and cost as a (name of your favorite) $3K DAC! 
I agree there is a bunch of hoop-la. There is some differences in sampling rates and such with Mac gen 2 dacs.  It had something to do with SACD sample rates, and the DACs ability to use ALL of it. 
Macs second gen Dac addresses that along with their, $$$$$$$$$$
Transports.
Someone will clear it up.. To rich for my blood. I'll stick with my (ES) Sonys, thank you very much. I love the bang for the buck and the house sound of the TWO, Sony and Mac..Gen 1 Dacs, both fine by me..

Regards
just to be clear, the USB input on the AXA25 and AXA35 are charging ports, and they do not contain an internal DAC...
Come on guys some of this is parts cost and quality also. A quality and purpose built chassis that reduces unwanted vibrations costs and takes engineering. Some use $250-$300 chokes from Lundahl and use 5 of them! Some use $15 resistors and $150 caps in key positions. Some use very high quality circuit boards. Some use high end trannys that can be very expensive.

Some use Opamps at $35 a pop. Some use the best wire at $4 - $10 foot. Some are hand made one at a time taking up to 5 days to complete. Just the power supply in a well made high end dac will have parts cost 100x the Topping dac. Now we can talk about the use of high quality input and output jacks, IEC and such. I could go on and on, but you get the point.