3x is a wide margin. I remember seeing numbers at my last contract job that suggested it was close to 1.75x and was using that number in the process of getting hired directly. I knew the companies costs to hire could be under that 1.75x value but still be a pay bump for me especially as I didn't have any benefits through the contractor saving them costs with no return to me.
For the contracting agency the value of my labor to a third party is how they make money. Seemed simple enough to me but not a racket I wanted to bounce around in.