Estimating Infrastructure Costs for Outbound Campaigns with a Pay-Per-Qualified-Lead Model

Hey guys. Need a little help in client acquisition. I am talking to an agency owner who has 7 clients. he wants to run outbound campaigns for them. I am in conversation with him, however he wants to know the infra cost before hands since he is pre revenue stage. Also, he wants to work on a pay per qualified lead model and he bears the infrastructure cost. However, it's sort of my first client interaction for this purpose. Please guide me about the estimated infra cost I should commit to get started