If your Epics (or Features) have a given budget that pays for the Scrum Team’s time spent on delivering it, like in any other good project, a governance/control of this budget is needed, apparently.

If this controlling accountability sits with anyone outside the Scrum Team, like a Project or Line Manager, transparency will be reduced for the team. Therefore, make sure to empower the Product Owner to also be the budget owner of whatever work the Scrum Team will do, so they always have the ability to adjust the scope to stay within budget if needed in alignment with the customer. 

Alternatively/ideally, start funding your products or Value Stream based on the cost of your teams—it’ll make life much simpler for everyone involved and help your organization save a lot of money through a reduction in administrative tasks.