I think you didn't post enough information...
What are the vms/containers doing? (I have a vm at work that is running sql server and requires at least 64 GByte ram, this single vm would already disqualify a bunch of "older"/single socket e3 xeon systems that support only 64GByte ram)
What is the "heavy load"? (This could define the minimum requirements for the system which could be over the budget of $400. See the this post why it's relevant:
https://www.servethehome.com/of-bbq-and-virtualization-large-nodes/)
Why ecc ram?
Location? (Shipping servers from Australia to Germany can be 300$+, this information is useless for everbody but people in australia & europe
)
Do you want to run "netflix at home" for 20+ concurrent clients? full hd? 4k?