What will be megar resistance value for LV cable like pvc xlpe and others that we can confidently say that is good cable

Depending on voltage rating & applied test voltages, most common LV cables rated up to  600V when applied with  1000V DC test voltage should give an acceptable result of  100 Mega Ohms or higher.

A good cable means good conductor, so a good cable will have comparatively low resistance and high conductivity.

For LV XLPE cables, the acceptable readings should be as follows to justify if the cable is good;

1. Insulation Resistance Test ≥1.0 MΩ2. Continuity Test ≤1.0 Ω

Usually use250V also. The result should be over500 Mh. But if can use1000 V, it is much better and result over100 Mh. is preferable.

Agree with Leonardo Banzali 

according to applying voltage