Seeking DAC $300

Shameless plug coming...I have a "spare" Kingrex DAC (USB-only) in perfect shape and would sell same to you for $150. I have box and all. This is the model UD01 Pro. It's very nice.

For that budget, the Schiit Bi-Frost would be hard to beat.

look into Audioquest Dragonfly $250.00 new

I was thinking a little more about it. How much SHOULD I spend? My limit at $300 is pretty arbitrary. Would I notice a lot of difference if I spent say $500? or $700?

There are excellent sub $300 DAC options at the moment. The new $99 Schiit USB DAC is one option, or the HRT Streamer DACs are solid in that price range. BitFrost and Dragonfly suggestions above are also solid. Used, you could get a USB only Tranquility DAC for a few hundred more. Really excellent sounding USB DAC, though it doesn't do hi-rez (24/92 or 24/192). Wyred4Sound also has some nice options in that range. I'd start looking at reviews of those, and hopefully you will be able to audition the ones that seem to best fit your preference and budget. A number of these are sold new by companies that have good return policies, or by online sellers who take returns (Music Direct for example).