PCPartPicker part list /
Price breakdown by merchant
CPU: Intel Pentium G3258 3.2GHz Dual-Core Processor ($64.89 @ OutletPC)
Motherboard: MSI Z97 PC MATE ATX LGA1150 Motherboard ($87.78 @ OutletPC)
Memory: Kingston HyperX Fury Blue 8GB (2 x 4GB) DDR3-1600 Memory ($45.69 @ SuperBiiz)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($52.33 @ OutletPC)
Video Card: MSI GeForce GTX 750 Ti 2GB Video Card ($110.99 @ SuperBiiz)
Case: Corsair 200R ATX Mid Tower Case ($59.99 @ Newegg)
Power Supply: EVGA 500W 80+ Bronze Certified ATX Power Supply ($34.99 @ Newegg)
Total: $456.66
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-10-15 13:11 EDT-0400
To explain with an unlocked multiplier cpu you can overclock the cpu (increase performance) but only if you have a motherboard that supports overclocking (from intel, chipsets with Z** or Z*** support overclocking, and also enthuiast X**). This gives more performance in cpu related tasks. It doesn't damage the cpu (and in terms of reducing lifespan: a medium oc let's say reduces cpu lifespan from 20 to 15 years, this doesn't affect you as you won't use the machine for so long) if it is done correctly an have sufficient cooling.
Here's a good build for your budget (it is over the budget because of the case (I picked the case thinking about upgradeability and alo the motherboard) ,you can pick a cheaper case (but this one is worth it).
With a Z97 motherboard you can upgrade to an i5 or i7 in the future and it is unlocked so you can overclock the Pentium. I picked good quality components for the build while also giving thinking about usability, upgrading and lastly looks.
P.S. The Corsair 100r and 200r are about the same price, so why not pick the better model.