Graphics Card
PowerColor Radeon R9 290 TurboDuo - $249
NVIDIA simply cannot get the pricing of its sub-$300 lineup right and continues to offer nothing compelling until the $310 GeForce GTX 970. The company may yet make a ton of money with their mid-range line-up, but that's only because of its better sales-force. The Radeon R9 290 TurboDuo from PowerColor is a gem.
At just $249, the Radeon R9 290 TurboDuo offers current-gen tech. Our tests show that the R9 290 is a whopping 52 percent faster than the $50 cheaper GeForce GTX 960 at 1920 x 1080 pixels, our target resolution. It also offers 4 GB of video memory. PowerColor added a factory overclock on top of that. If this doesn't highlight NVIDIA's terrible pricing for the GTX 960, nothing will.
When you're building on a tight budget, brute frame-rates gain much more weight over other factors, like power and noise. The R9 290 certainly won't beat the GTX 960 at the two, which is both slower and $49 cheaper, but that's a small price to pay for 52% more performance, a crucial factor once your machine starts to show its age as newer games get increasingly more taxing. There could be situations where 52% more performance spells the difference between "playable" and "slideshow."
Long-term driver support is pretty even for both NVIDIA and AMD, especially in light of the way NVIDIA is supporting its "Kepler" based GPUs right now when dispensing performance improvements.
Storage
ADATA Premier Pro SP610 128GB - $49
We will eat grass if we have to, but refuse to buy HDDs despite our low budget. HDDs simply can't cope with modern game-load and OS/app load times, and their better price/GB can't bail them out of that. An HDD would have made game load-times no different from today's consoles (which cache games on HDDs), which threatens the purpose of this build.
Over the years, ADATA has grown in brand-trust, availability, and after-sales support, and the Premier Pro SP610 128 GB is a good option at its $49 price point. This drive has the least overprovisioning in its league (with mostly 120 GB drives), and offers sequential read-speeds of up to 560 MB/s, with up to 66,000 IOPS 4K random-read. The write speeds of up to 150 MB/s are nothing to write home about, but you'll be reading a lot more than writing. You also get a license for the Acronis disk-imaging software.
Power Supply
EVGA 500W 100-W1-500-KR - $39
The worst thing you can do when building on a tight budget is to give in to the temptation to buy a generic PSU, or one that comes pre-fitted to your case. Many of those PSUs have no modern features (eg: APFC, single +12V rail, Haswell C-state support, etc), the right cabling, critical protection mechanisms, or worse, come with a tiny rear-oriented fan. The wrong PSU won't just damage itself under the duress gaming can cause as it will also take other components in your system out in the process.
At just $39, the EVGA 500W (100-W1-500-KR) is almost altruistic, coming from an enthusiast brand such as EVGA. It has everything you and your build will ever need - a fan in the right place, active-PFC, electrical protection mechanisms, sleeved cables, a single +12V rail design, two 6+2 pin PCIe power connectors, and a 3-year warranty.
We're now left with $243.