Apple iMac 21.5 inch Mid 2011 Core i5 - needs hard drive/OS

Apple iMac 21.5-inch, Mid 2011 (A1311), Intel Core i5 quad-core.
Powers on and the screen works fine (no lines or dead areas), but it shows the "folder with question mark" at startup, so there's no bootable system. It needs a new hard drive/SSD or a macOS reinstall. With an SSD this is still a decent machine for browsing, YouTube, Office or kids.

– 21.5" Full HD screen, built-in FaceTime camera & speakers
– 4× USB, Thunderbolt, FireWire 800, Ethernet, SD card slot
– Power cable included

Cosmetic: small chip on the glass at the bottom-left corner and some scratches on the back (see photos).
Please note: this is an all-in-one computer, NOT a monitor. It can't be used as a screen for a laptop.

I also have an older iMac 21.5" (2009). Take both for €65.

Collection only from Clondalkin, Dublin 22. Cash or bank transfer.