do you know what resolution your cameras are ? for a DVR you mostly just need the resolution to match what your cameras are.

cheap DVRs are available on amazon, for example https://www.amazon.com/ZOSI-Surveillance-Recorders-Standalone-Detection/dp/B07LGX7VWM

you'll need a HDD, for example https://www.amazon.com/Purple-2TB-Surveillance-Hard-Drive/dp/B071RM2HS7/