Budget next gen gaming PC

Mac, and Apple in general, carry a premium because of the company and it's reputation or whatever.

You can do a better job building your own computer and if it's just for gaming (as opposed to serious video editing/encoding and the like), you can make a great gaming computer with AMD parts.

To start, you want a case with good air flow and usually you'd like one that can be upgraded with (for example) additional fans and has room for liquid cooling or a large heatsink. You'll want a mid tower case like the Antec 300 or something similar (the Antec is about 60 bucks). You'll have to look into compatibility with liquid cooling and your choice of case.

A great processor that's very adjustable is the AMD FX-8320
http://www.newegg.com/Product/Product.aspx?Item=N82E16819113285
159.99 right now, but you can get it on promotion at times for 139.99 or packaged with a game or something.
Eight cores may be a bit much, especially if you don't multitask, so you can go with one of the cheaper six or four core processors that are anywhere from 79.99 (via promotion) to 130 or so.

A motherboard that is compatible with that would be anything with the AM3+ socket. I have the 990fx chipset and it gives me a lot of options, but if you aren't such an enthusiast and aren't going to overclock, you can go with something cheaper like the 970 chipset included on this:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131872

A great graphics card is REALLY the core of the machine and there are cheap, new ones out there like this:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150686 or the HD 7870 which is close in performance and usually cheaper.

You will need a power supply with sufficient amperage on the 12V rail to power the ensemble and you will get a great one from the OEM if you choose something from Seasonic like this:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817151137

Then you will need RAM that provides both a high frequency and low latency and delivers it at a low voltage
like these from G Skill which have a 15% discount at the moment:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231460

And you will need a fast and reliable hard drive like this from Seagate:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822178381

All this to total you in at a little under 800 dollars.

If you're a student, you can get your copy of Windows 7 Pro or 8.1 Pro for free (or at a significantly lower price).