If you plan to build a budget NAS and enough room is not a problem, I personally would recommend to get an old and used Dell T20 Xeon E3-1225v3 with min. 16GB ECC DDR3 RAM, 2x10TB Seagate Exos ZFS RAID and a bootable USB Stick with TrueNAS or if you prefer Linux, TrueNAS Scale / OpenMediaVault.
If room IS a problem, you could get a HP Microserver Gen8 or higher with a Xeon the config above.
- Server Cost: 150 Bucks
- Total Cost: 650 Bucks (150 for server, 500 for HDD)
- Power Consumption: 33W Idle, 60W Heavy File Transfer
- Silent enough without modding the fans
- Ethernet-Transfer-Speed: 110MB/s on 30% System Load
I do not own a 10Gbit ethernet card, but I'm pretty sure, transfer speeds with 10Gbit would be acceptable, too.