I've tried to explain this exact concept so many times. Regardless of how cheap the parts themselves may be, in the end, it will be hard to outperform a game console when compared dollar to dollar with a PC of approximately the same power. Sure, the final price of building your computer when looking at nothing but the price of parts after rebates may be around $350, but that doesn't factor in shipping, a monitor, accessories you may need, the OS, anything like that.
When it comes to the monitor, sure, you can just use a TV, but at the same time, a lot of TVs are pretty shit computer monitors. They may have resolution issues or otherwise that really just make them shit for using an actual computer, whereas game systems work fine. That means that, regardless, most people are probably going to tack on an additional $150 or so grabbing a decent budget monitor. I don't need to buy a new TV for my game system. I already have it for movies and otherwise.
Even then, why in the hell would you build a computer that's simply on par with a PS4 or Xbox One? People complain so much about the systems being too weak, you would think a build like that would be avoided since you wouldn't be able to take advantage of a lot of the perks of PC gaming, like higher resolutions, unlocked FPS, and otherwise.
PC gaming is expensive to start in on. Anybody who says otherwise is a god damn liar. It can be cheaper in the long run when you're simply incrementally updating every few years with a new GPU here, a new CPU there, maybe replacing the mobo at some point, the RAM if you need faster or more, etc., but the cost of entry should not be understated. You have to be ready for a somewhat hefty first investment if you really want to take advantage of PC gaming.
For me, I just use my laptop. It has a discrete GPU, and is strong enough that stuff like New Vegas and Skyrim vanilla run on Ultra High without any tweaking. It fails pretty miserably with 2015 AAA, but that's why I have my PS4. It strikes a nice balance, and I ultimately only paid $850 between the two for the versatile nature of a PC that I needed anyways and the easy to use nature of a game console.
