relevant cost of labor

Question) A new project by BLW company would require 1000 hours of skilled labor. The current work force is already fully employed but more workers can be hired in at a cost of $20 per hour. The current workers are paid $ 15 per hour on a project that earns a contribution of $ 10 per hour. What is the relevant cost of appraisal to be included in the project appraisal?

Solution

Option 1 Buy in new workers $ 20 / hr * 1000 labor hours = 20000$

Option 2 Divert existing labor ($ 10 + $ 15 / hr * 1000 labor hours = 25000 $)

Option 1 is the cheapest so that is relevant.

Query: For option 2, if we divert existing labor, we lose contribution of $ 10 per house so that is relevant. But we no longer have to pay $ 15 / hour because the existing project is probably discontinued to focus on new project. So should we not take this as a cash inflow ( avoidance of an outflow) ? it should be (10*1000) – (15*1000) = -5000$ benefit