500$ is more than a enough for decent gaming rig.

The pentium is a bit weak for modern games but it offers much more upgradability than AMD cpus in similar price range.
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Pentium G3420 3.2GHz Dual-Core Processor ($71.99 @ Mwave)
Motherboard: MSI H81M-E33 Micro ATX LGA1150 Motherboard ($44.99 @ Micro Center)
Memory: Kingston 8GB (1 x 8GB) DDR3-1600 Memory ($54.99 @ Amazon)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($54.99 @ NCIX US)
Video Card: PNY GeForce GTX 650 Ti 1GB Video Card ($115.66 @ Newegg)
Case: NZXT Source 210 (Black) ATX Mid Tower Case ($37.99 @ Micro Center)
Power Supply: Corsair Builder 430W 80+ Bronze Certified ATX Power Supply ($19.99 @ Newegg)
Operating System: Microsoft Windows 8.1 (OEM) (64-bit) ($89.98 @ OutletPC)
Total: $490.58
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2014-04-12 10:26 EDT-0400)

Yeah 400-500 Is cheap for a gaming pc.

Heres my build:

http://pcpartpicker.com/user/Doision/saved/4lhl

Its not too expensive and it's a beast

For $400 dollars dont expect too much performance, your looking at a $700 computer minimum to make a good gaming pc, $400 can get you a decent one but it wont be anything special

They are all horrible. Build your own. But if I had to choose I would go with the second one.