In case anyone's interested, it looks like Boost Mobile has a $79.99 promo going on this phone:
https://www.boostmobile.com/?INTNAV=TopNav:Android#!/shop/phones/moto-e4/features/
Of course, if you purchase it from Boost it would not be unlocked, aka carrier agnostic -- but if you don't mind the Sprint network (with, I believe, up to 50 minutes of non-Sprint roaming included at no extra charge each month) that probably wouldn't be an issue.
Don't know how long it will last, but that's the best price I've seen so far.