Today, the ISPs are looked-for offering differentiated services with an adequate QoS for their end user. This is due to the fact that end users are not expecting the same QoS depending on their activities and consequently are not willing to pay the same price for these services. In this context, this paper proposes a new pricing mechanism that takes into account the customer behaviour to calculate the price of Internet services usage. The idea behind this approach is to optimize the network resources usage as well as the ISP profit by adapting, for each customer, the price of each service according to his profile. Hence, the proposed pricing mechanism is integrated into a dynamic SLA negotiation process. This process is divided into two steps: Pre-service SLA, and On-service SLA. The impact of our pricing model in over-provisioned networks has been analyzes analytically. The obtained results demonstrate that our mechanism diminishes considerably the cost of the over-provisioning. This is obtained thanks to a good balance of the traffic load during a day-scale period.