Well, fortunately I was running 10.10.4. Apple used to update OS info in the Community Forums whenever I upgraded, but I guess we have to do that ourselves now.
So now that we have established which OS I am running, I don't know what you are smoking, but a Hard Drive costs between $50 to $500 for what I want. But I wanted to see how much Apple would charge to replace mine, since it needs to be about the same type of drive due to the heating sensors etc.
A refurbished iMac like mine will cost at least $800, and that is for a basic bare minimum hardware.