ROI averages don't apply. Joint agreement is necessary between the supplier and customer on the costs and benefits in order to provide a trusted ROI.
ROI is not a game to produce a number. It's about quantifying and substantiating ongoing costs and benefits from a project - that are tailored for the customer.
Those working with something else to gain from the project; Consultants, external analysts - may not objectively assist the sale or provide a rapid evaluation of the proposal.