If you have a Mac, and NAS will do - you can set timemachine to back up to it. I use a (very old) Netgear Stora with 2x 2TB drives in RAID 1. It's one of the cheapest options around and can be rooted to enable a bunch of additional features. I've then got a second local drive (an old Seagate 2TB USB 2.0 drive) as an extra layer. It works pretty well as I'm in an office at the bottom of the garden, so the Stora backup runs up my gigabit ethernet back to the house, and then I have the USB backup drive sitting under the desk.
Another option is simply a basic NAS - theres really no need to go overboard and spend £150+ as you likely only need 2x drives in software RAID 1 for a backup solution.
Whatever you get, make sure its either USB 3 or Gigabit ethernet - you'll be replacing it in 24 months if it isn't.