To get started I would suggest the AudioQuest Dragonfly Cobalt. and a minijack to RCA Y cable and some RCA cables long enough to reach your stereo from your listening position (or just use headphones). If you find you enjoy streaming and you want even better sound quality It will probably cost much more than $500. (heck the interconnects are over $500 if you buy them new).
The streaming services have free trials which will really open up access to so much music. Headphones and the dragonfly will surprise you on how good streaming can sound.
It's taken me over 5 years to get to my current digital setup and comparatively I didn't go the conventional route. I've learned so much about what makes a difference in the sound during the process and I believe my digital system currently outperforms the dollars invested even factoring in all the Bluetooth, Chromecast, Raspberry PI avenues I pursued to get to where I am today.