The answer is not simple. Try to match the camera manufacturer to the NVR or you might have problems. It varies.
If you buy junk brands, you will have poor results.
All that money on what? There is usually a reason that a company can demand a premium for their product. Not all cheap china cameras are the same.
What cameras are you trying to use?
With some cameras the motion detection will not work with the dahua NVR. You will only find out if you try.