Quite a good NAS on sale from TerraMaster if you're after something on a budget that'll do all the essentials including network storage with RAID redundancy, Plex transcoding, Docker, video surveillance, syncing to OneDrive/Google Drive/Dropbox and more. While the OS isn't as mature as others you can still others including Synology DSM (Xpenology), Unraid, TrueNAS, Windows and more.
Featuring 4 SATA bays, 2x M.2 2280 NVMe slots for storage/cache, 2x 2.5GbE LAN ports, Intel Celeron N5095 quad-core CPU, 4GB DDR4 SODIMM RAM (upgradeable to 32GB), 2x USB 3.2 Gen2 10Gbps ports and HDMI (for command input).
Alternatively you can get the newer F4-424 NAS with an Intel N95 CPU for $607.99 delivered.
Last time I checked you can still get a free 4GB stick of RAM by posting a review and sharing it with TerraMaster. For HDDs I recommend checking out East Digital for cheap enterprise drives.
The hardware is solid, but the Terramaster OS (TOS) is pure garbage written by amateur developers mimicking established NAS OSes. If you get one of these, install another OS straightaway. TrueNAS if you need high availability and maximum data integrity, or Unraid for home media server applications. You just need to replace the built-in USB bootloader with your OS of choice, change the boot order in the BIOS, and increase the PWM fan settings.