My current config:
Fujitsu D3417-B12
Intel Xeon 1225
64GB ecc
WD SN850x 2TB
mATX case
Pico PSU 150
For backup I use a 2TB enterprise HDD and ZFS send
For snapshotting i use zfs-auto-snapshot
So really nothing recommendable for buying today. You could go for this
https://www.aliexpress.com/item/1005006369887180.html
Or an old Fujitsu Celsius W580 Workstation with a Bojiadafast ATX Power Supply Adapter, if you need harddisks.
Unfortunately there is no silver bullet these days. The old stuff is... well too old or no longer available and the new stuff is either to pricey, lacks features (ECC and 2.5G mainly) or to power hungry.
A year ago there were bargains for Gigabyte MC12-LE0 board available for < 50bucks, but nowadays these cost about 250 again. These boards also had the problem of drawing too much power for an ultra low power homelab.
If I HAD to buy one today, I'd probably go for a Ryzen Pro 5700 with a gaming board (like ASUS ROG Strix B550-F Gaming) with ECC RAM, which is supported on some boards.