How much does a DAC do the more expensive it is?

All DACs are defined by their output stages, for good or bad.

Anyone that thinks a $20/30/40k R2R or Delta Sigma DAC is going to provide audio nirvana based on it's process/processor is seriously misled.

The current Delta Sigma chip is the ESS 9038 Pro with the ESS 9039 Pro due to debut maybe this year.

Unless controlled listening tests are done all bets are off! A DAC is really just a sound card - and needn't cost four and five-figures! 

While technology may be different, DAC's do about the same thing regardless of price, in terms of specs at least.

I don't know if price is the right differentiator either.  Use your own ears to determine value, not the price tags or reviews. 

I have not explored transports with streamers...in controlled tests the Cambridge CXC was clearly preferred to the Oppo 103...no controlled tests for the 105 as it is used in my home theater, though I quickly tired of it as a streamer for Tidal...I do very much like the SACD Marantz 30n; CD player, DAC, Streamer, that I use in good quality home office system...while price doesn’t guarantee you will like any product, I do unfortunately find the gear I like the best does tend to be more expensive...though I do find Schiit products and other direct sale manufacturers to be excellent values...it’s whatever you like best and decide is the best price for you...

Unless controlled listening tests are done all bets are off

When you use your own ears to judge, the "controlled listening test" is done - All bets are on!