See cost changes alongside the milestones they affect.
Use the same structure for plan and actuals
Group the planned budget and actual costs into the same work packages. A shared structure makes it easier to understand whether a variance comes from a changed scope, a different rate or work that has moved to another phase.
Record changes before approval
Capture what changed, why it is needed and which milestone it affects. Identify the person who can approve the change. A cost without an owner or an explanation can be difficult to assess when the team is under time pressure.
Review cost and schedule together
A cheaper option may take longer, and an accelerated delivery may cost more. Bring both effects into the same discussion. Keep the approved decision and supporting information available for the next review.