SubjectVerb agreement

which of the following statements are grammatically correct and in which condition (Eg: considering subject/verb as singular/plural)?

1)The cost price of all the items is same.(am considering Item1:CP , Item2:CP and so CP is same ).

2)The cost prices of all the items are same.(am considering Item1:CP1 , Item2:CP2 and CPs (CP1,CP2 ) are same).

3)The cost price of all the items is different.(I don't know whether it is grammatically correct and can't think of a possible use case )

4)The Cost prices of all the items are different(am considering Item1:CP1 , Item2:CP2 and CPs (CP1,CP2 ) are different)..