The costs of support will vary enormously depending on the approach that is used. The key issue is to ensure there is sufficient funding available to cover all the costs, for example time for staff and members of the public, venue / room hire and travel costs for people to attend group meetings.
It’s important to build in all the relevant costs for support in any funding bid for a project with public involvement. You need to be clear about which individual is responsible for providing support, how much of their time is being allocated to this role and what resources they will need.
Do not underestimate the time needed to provide support – it might require a full-time staff member within an organisation, or frequent meetings with individual members of research teams.