We present a generic step-by-step methodology for evaluating the total cost of migrating from a capacity-exhausted WDM network to different upgraded alternatives. The presented methodology is the first effort to provide a generic evaluation framework (allowing the evaluation of scenarios with different traffic growth rates, optical technologies, network architectures, and resource allocation algorithms) that considers both capital and operational expenditures of the upgraded alternatives to then identify the lowest-cost option. Previous works have just evaluated specific scenarios or only CapEx or OpEx (not both). As a way of illustration, the proposed methodology was applied to compare the migration cost of two upgrading scenarios. The methodology allowed identifying the lowest-cost alternative, categorizing the key cost factors of CapEx and OpEx, and evaluating its impact on the migration cost. Surprisingly, results for the study case presented show that migrating to an automatically provisioned network does not necessarily lead to cost savings.