EDIT - Comments are saying that these are potentially locked to Verizon / Xfinity. Apparently their policy changed from being unlocked from purchase to a minimum of 60 days. I ordered one so we'll see how it goes, but 30 day returns and 90 day warranty as a fallback.
As the title states, refurbished (pre-owned) iPhone XR 64GB Black on VIPOutlet's eBay store. Currently $419 but 20% off brings it to $335 + tax, no contract, no payments, no renewals, etc.
I've always had good luck with VIPOutlet - bought my XM3s, CH700s, and a bunch of other stuff from them without any issue.