Struggling with Plural/Singular?
The first one is incorrect.
The value of cars depreciate over time.
The verb should agree with 'value', not cars.
For this reason, the 2nd and 3rd ones are both correct. Their usage depends on context.
Consider:
The values of (most) cars depreciate over time.
Values of different cars
and
The value of (my) cars depreciates over time.
Value of all my cars taken collectively