It will be cheaper for companies to buy copper membership and manage their campaigns by themselves but they will have to spend more time building trust within the community before they can be recognized.
You might be right but I could not agree with you. To run a signature campaign they do not need to be reputed. Hence they are not aware of the signature campaign, signature design, creating spreadsheets, and calculating that. If they have all the ability then their time might be more valuable than the spending on the campaign manager. If a newbie run a signature campaign and escrow their fund for few weeks then they have nothing to be worried about.
Well at the end its a business so the companies will always approach the members who is already doing that job and managing the campaign on their own and escrowing the funds may be disastrous for the money they are about to spend because they can buy copper membership but they may have no idea of who to hire but managers generally do have an idea of which kind of members will fit for the project they are going to promote so they will hire accordingly.