Cloud brokering service, as an intermediate between providers and end users, ensures various comprehensive functions in both senses. These functions include, amongst other, service consulting and aggregation, cost optimization and pricing. Security is now becoming an arising need to be handled at the same level. It mainly consists of providing access control to the cloud, compliance with security policies and protection against threats. This implies additional costs to providers that need to be optimized. In this paper we address the security cost modeling issue in multi-broker cloud architecture through an innovative set of functions to be implemented by cloud brokers in a distributed way in order to evaluate and optimize the cost of implementing a predefined security policy. Furthermore, we carry out an analysis that aims to draw up different investment schemes in function of the investment time horizon and the investor profile. By simulations, we study the impact of this cost on the profitability of cloud investments through a financial analysis which uses the DCF (Discounted Cash Flow) method.