The Risk Management Plan is part of the Project Management Plan, which is developed in the Planning Stage before the Execution Stage.
And the first process of Risk M. Plan, is to define (predict) different risks that may happen in the project life cycle, and develop the appropriate action(s) to deal with this risk.
Some examples of the cost-related risks associated is anticipated change in the price(s), taxes or even currency exchange rates along the project life cycle. Which in turn impact the project costs.
Therefore, some strategies to be developed and identified in the Risk Management Plan, stating the required action(s) in such cases.
For this reason, the Risk M. Plan is developed prior to Cost Estimate Completion.