Asrock Rack c246 WSI (Mini ITX workstation board) 32GB DDR4 ECC Udimms (16GB x2) Core i3 9100T (25w, low power 4 core part, supports ECC, and quicksync) 6 IronWolf 4TB NAS drives
The 6 drives are in RaidZ2 so give 16TB usable space, and at full pelt the max power consumption is 60W for everything.
Servers are more efficient than people give them credit for. It's close to a gaming PC in electricity usage. Certainly not 60W (or what people can get with NUCs and RPi clusters) but for the power I get, it's very much worth it.
Edit: But even at $500, that's pretty much the price of a low-spec VPS or VM per year. So for a fairly low initial price to buy the server, you're getting far more performance for the same price you'd pay someone else to use theirs.
Since it's a home server, when it's not receiving backups from computers in the house, or streaming media via Plex it's sitting there at < 15w, which is low enough not to worry about.