This research focus on the problem of modeling and optimizing the time-cost trade-offs in project planning problem with taking into account the behavioral impact of planned human resources. As a distinct from the original Goldratt conception and heretofore research results and known applications we proposed an approach taking advantage not only from task duration overestimations, but primarily from overestimations of amounts of work expected to its completion. Proposed problem description contains both safe and reasonable amounts of work estimations. At the recent stage of research we introduced the influence factors matrix with the possibility of flexible resources assignment. The model uses a mechanism of motivating the resources through the creation of bonus fund from the pool of savings. Theoretical considerations are illustrated by the numerical example.