If you want to build a non-blocking Clos network of 2N ports with switches with N ports you need to take 4 switches in the front with N/2 ports and 2 switches i

If you want to build a non-blocking Clos network of 2N ports with switches with N ports you need to take 4 switches in the front with N/2 ports and 2 switches in the back interconnecting all the ports to the back for a total of 6 switches, so not even including cables a modular switch providing 2N ports is worth 6x per port than a fixed switch... The number are a little better for bigger but approach at a cost per port of 3x per port not including cables. In my experience modular switches are more in the ball park of 2.5-3x per port. I am not including other possible benefits that modular switches can have non-blocking fabrics.