I switched from Mountain Lion to El Capitan and it only cost me $500. It kept crashing after I upgraded so I took it to the Geek Squad. Had to purchase a service contract ($200+) but they said it was a hardware problem and Apple had to fix it. Took it to the Apple store (where I should have taken it in the first place, I know) and, sure enough, it had suddenly developed a bad video card just at the same time I upgraded. Imagine! That only cost $300+. Now I just have an upgrade reminder in the App icon telling me to upgrade IPhoto which no longer exists. I am not rocking the boat with that one.