Factor in the cost of your normal PC (you probably have one, and you probably are going to have to upgrade it some time in the future) and online gaming, and it could be quite different already. Then there's the fact that your old input devices (mouse and keyboard) are probably good enough so you don't need to get new ones, and your old OS could be good enough (depending on your old PC's age). And finally, the most obvious part: PC games are cheaper, and if you're willing to wait, you can get PC games for almost nothing.
Of course the total price depends quite a bit, but overall, PC actually has a chance of being even significantly cheaper. And in some cases, consoles can naturally be cheaper too.