Is low cost DAC worth it?

A minimum of $750 and up keep in mind a $800dac has under $200 in total 

including the box that’s roughly the average , audio cables much more so still.

Can’t go far wrong with the musical fidelity v90 dac. Stereophile high class B, low class A component. I’ve had mine for Years and I love it.

I have a Bluesound NODE streamer and a Denafrips Are II DAC.

Given your budget, I would suggest that a used NODE (which has a built-in DAC) would give you the most bang for the buck.  Especially if your hearing or system isn't top-notch, you'll find the NODE's DAC quite satisfactory, and you can continue to stream via wi-fi--the NODE is really designed to work well that way, and it does when you give it a strong wi-fi signal.  The smartphone app for the NODE can also tell you the wi-fi signal strength it is receiving, so you can know whether it is strong enough to stream high-resolution files or just CD-quality files.  And I can hear that hi-res files sound better than CD on the NODE, even using its DAC.

$500 DAC - nope.  Better off spending $500 and upgrading your CDP instead.

A good budget DAC should be a step up from the one in the Airport Express.  Topping, SMSL, and Schiit all have well measuring and nice sounding DACs in you budget.