QNAP Surveillance Station is quite heavy on the RAM demands - but with 1GB RAM it would run OK, using maybe 600MB for a couple of cameras.
The TS-221 comes with a base of 2 free camera licences, additional licences are $60 each.
For connecting as a 'NetHDD' to Hikvision cameras though, it does offer useful flexibility with NFS and SMB/CIFS shares.
It's in the 'SMB' class of QNAP NAS, so supports the 'flexible volume management' capability to create storage volumes of arbitrary size, which the NeHDD capability of a Hikvision camera requires.
For that price, and with the HDDs, that sounds like something worth buying, in my view.