I mainly play Dota 2, but wanted a good budget gaming PC for the next 3-4 years that could also run the occasional AAA title at 1080p 60fps. I am fortunate to be close to a Micro Center. I deal hunted for 4 weeks with a budget of $500. All prices listed are the total price plus shipping and tax (NJ).
CPU: Got from Jet.com. I had no doubt that I wanted to build around this CPU. I was initially also thinking about waiting for the Ryzen 3 1200, but ultimately went with the G4560 (didn't think AMD would match the G4560 in price-performance ratio). I was lucky to find these just restocked on Jet ~2 weeks ago. Used the 15% off code (SAVE15).
MB: Got from Micro Center. Great budget value board in my opinion. Had exactly what I needed for my build (B250 aka Kaby Lake-compatible, no BIOS flash upgrade needed). It also has 2 Ultra M.2 slots for future SSD additions, which is particularly helpful to me (see: Case).
RAM & SSD: Got from one seller on /r/hardwareswap about 3 weeks ago. The SSD is well known for being a budget-friendly SSD. Its performance is close but inferior to that of a Samsung 850 EVO. A brand new MSRP version of this is easily double the price. In regards to the RAM, I knew I wanted DDR4-2400 for the B250 MB. I was initially thinking just 1x8GB for ~$60, but couldn't pass on this deal.
GPU: Got from Micro Center. Without a doubt the RX 470-580 line is extremely difficult to find thanks to the cryptocurrency market. Speculation that some miners would give up on Ethereum and return their cards by the end of this month had me scouring Micro Center's OPEN BOX section like a hawk. I was fortunate to grab this as an OPEN BOX deal from MC last week.
Case: Got from Newegg. This case goes on sale relatively often from what I've seen, but it's price was definitely at its lowest during the Amazon Prime Day/Newegg FantasTech sale. Newegg had this listed at $29.99 (MSRP $129.99). In my opinion, a great case. Comes with front 140mm and back 120mm fans. Dust filter on top of the case (if you're interested in adding a radiator top-side or two more fans), as well as a dust filter for the PSU. Only problem I have with this case is that there is only 1 SSD mount (on the backside behind MB), but it's a minor inconvenience. Motherboard has 2 M.2 slots, so any plans to add more storage will involve them instead of 2.75" drives. This case is also awesome for those who have and wish to connect multiple 3.75" HDD to the MB.
Power Supply: Got from Amazon. Amazon had some "free cash" deals (i.e. Using their phone app, adding cash via CVS, and using their Chrome App), which resulted in a free $25 to use towards the PSU. The last build I made was around 10 years ago; I was not surprised to see that SeaSonic was still one of the most reliable PSU companies around. 500W is plenty for my build, and I wanted modular.
Other: Got this from Amazon Prime Day as a lightning sale. Still pretty cheap option to get if you needed WiFi. Router is in the living room, and running an ethernet cable to it is not an option. Link: https://www.amazon.com/ANEWKODI-600Mbps-150Mbps-433Mbps-Wireless/dp/B01G8IPLD8
Final Comments: I did go a little bit over budget, but am very happy with this build.