I previously had a Ryzen 5 2600 (Zen+) and now have the 3600 (Zen2) and I have been very happy with both. I was able to find the 3600 for $174 but prices vary over time.
My reasoning is that I wanted the fastest, reasonably priced processor at 65W TDP. Folding@Home on my RX580 already has the temperature in my office 10 degrees F hotter than the rest of the house.
Having been a packager for 12+ years and building a lot of software on my PC, I can tell you it's plenty fast paired with DDR4 3200MHz memory (memory speed affects the optimal infinity fabric speed and has a significant impact on performance but that's a whole thread on its own).
Right now i have it in my X370 MB and works fine after a BIOS update. If I were going to buy right now and didn't care about Zen3 compatibility I would buy a B450 MB (may or may not get updated BIOS from MB manufacturer). If you are worried about upgrading to Zen 3 when it's best to go with a B550 or X570.
Thanks, Richard