I originally paid $64 for this trackball at Staples back in 2002. I'm impressed at how the value of this mouse, used, has gone into the hundreds. Yet, I'm not surprised. This is an amazing trackball because it involves the movement of any 2 of the 3 leftmost fingers of the right hand. This means your hand won't get into repetitive motions that may cause permanent damage later on. I have been using this mouse for years and it's still going strong. You just have to clean the ball and lenses once in a while. My mouse is PS/2 but I am ordering a converter (PS/2 to USB). Many attempts to convert me to other models have failed. My hand is completely comfortable and the buttons fall naturally where the fingers rest. Truly perfect design. I just can't believe it has gone up in price over the years, yet I can understand why. A true investment in the health of your hand, fingers and wrist. Totally worth the money.