Refurb4Less via eBay offers the refurbished HP Pavilion 590-P0050 Intel Coffee Lake Core i5 2.8GHz Desktop PC for $409.99 with free shipping. That's the lowest price we could find by $40. Features include:

Intel Core i5-8400 2.8GHz Coffee Lake 6-core processor

8GB RAM, 16GB Intel Optane memory, & 1TB 7200 rpm hard drive

DVD burner

Windows 10

Note: It's covered by a 90-day warranty, although it's unclear who backs it.