Fully-transparent DWDM networks working at 10 Gb/s or more have limited reach. At these high rates, only translucent networks able to fully regenerate the signal when needed can be used to implement long haul transport networks. Since signal regeneration and regenerator placement can be done in many ways, an effective design procedure will target the overall cost minimization. In this paper, we propose three regenerator placement procedures. Two of them minimise the number of regeneration nodes, whereas the third method minimises the total number of regenerators. Moreover, we present an economic model aimed to evaluate and compare the overall cost of these procedures. We show how to choose the optimum regenerator placement method according to regeneration type and associated costs.