Cost Planning

If one is to map a project with WBS elements and network activities. If there is a case where certain WBS element will be required to be planned with an overall cost with the activities assigned to it not requiring cost planning. Again the other WBS elements are such that are assigned with activities that would need cost planning. Then in such a case will it be ok to go ahead with Easy Cost Planning for the WBS elements requiring an overall costing and activity costing for the latter? In short can both Easy Cost Planning and acivity costing be utilised simultaneously.

Dharmendra