What is a decent, cheap gaming laptop?

Not possible, sorry.

Cheap, decent gaming, laptop.

Pick any two.

The reality is, a gaming laptop is 1/2 to 1/3 as powerful as a gaming desktop for the same money. A $450-500 gaming desktop won't play DayZ or Arma at decent framerates, so a $500 laptop certainly won't.

Look on Craigslist and maybe you can find someone's used laptop a few years old, but that is a long shot, and it probably won't last long.

If you want something cheap to play games on, buy a PS4.

Gaming laptops require a lot of power and cost more than your budget.

Here are a couple of articles that may help.

Cheap Gaming Laptops
http://www.pcmag.com/...410,00.asp

Buying Guide: 10 Best Cheap Gaming Laptops
http://www.computershopper.com/holidayguide/2013/buying-guide-10-best-cheap-gaming-laptops

Fortunately the games you want to play are hot very demanding. You need to find a laptop with a processor more powerful than the desktop i3-530. You can use this chart to see which ones are better/faster.
http://www.futuremark.com/hardware/cpu

For graphics ability, you need something which will outperform the AMD HD 4870. Again, use the following chart to narrow down your selection.
http://www.futuremark.com/hardware/gpu

The top laptop mfgs of windows laptops are, in order, Lenovo, Asus, HP, and Samsung. I would not recommend purchasing a Dell without fairly thorough investigation of that particular model - mostly reviews. The others are rated so poorly that you should avoid them, particularly Acer, Gateway, and Toshiba. Avoid the Essentials line of Lenovos but all the rest are great.

Those games are very resource consuming.
You can't buy something with that money that will run those games amazingly. I suggest buying a cheap desktop and getting parts. Desktops are much cheaper and you can build a good rig from it.