So, this is the first PC build I've made myself (I was 21 at the time). Coming back to PC gaming from a 5-year Mac experience (which was great, don't get me wrong, Macs are awesome, but I really missed proper gaming), I essentially had to educate myself from scratch when it came to relevant PC hardware. From the start, I've decided that I wanted to focus on upgradability down the line, and, since I didn't have a huge budget (around $800 I made from selling the Mac), I skimped on components I felt I could painlessly upgrade later. So, here it goes:

CPU (Core i5 7600k): the most sensible choice for gaming at the time, and will probably serve me very well for the next 5-6 years. Even a cheap tower-size air cooler (I went with a Zalman CNPS10X or something) should give me a ton of overclocking headroom should I need it. 8th gen hadn't come out for another month, and I felt like I didn't need more than 4 cores anyway. Even though it doesn't match up too well with the GPU (more on that later), I wanted a slightly overkill CPU because it's the hardest component to replace: if you're CPU-bottlenecked, you're pretty much doomed to rebuilding the entire system.

Motherboard (Gigabyte GA-Z270-HD3): the cheapest available Z270 board at the time. Has everything you would expect from a modern mobo, including an NVMe M.2 slot.

Memory (generic Crucial 16GB): I specifically didn't want "gaming" RAM, since I don't see a benefit in going higher than 2400 and the price premium is insane where I live (Russia). Went with one 8GB stick, then 4 months later added another one. I believe that'll be enough for some time.

Storage: (Samsung 860 Evo 500GB + Seagate Barracuda 3TB): there the story is a bit more comlicated. I started with a 120GB cheapo Transcend SSD (adhering to my philosophy of leaving room for upgrades) and a 1.5TB WD hard drive I had remaining in the basement for games/videos. The hard drive was rapidly dying, and so I quickly replaced it with a new 3TB Seagate drive, which works to this day. As for the SSD, I finally upgraded to 500GB as a New Year's Day present, which populated my M.2 slot. It's not NVMe, but I don't see the point of paying the premium if I'm not doing anything special with it.

GPU (MSI GTX1050Ti Gaming X): I got a bit unlucky there, as I built my system at the height of the cryptomining craze, and as such GPU prices were in the stratosphere. This was the last component I bought, and so I was under a rather strict budget of about $170, which was just enough to buy a lightly-used 1050Ti. Today I could've easily afforded an RX580 8GB for this kind of money, but I digress. It's enough for me for now, and it's an easy upgrade later if I want.

Case (GMC Arena): this Korean manufacturer is so unknown than I don't see it anywhere, not even PCPartPicker. It's a cheap, $25 black-box kind of case, nothing to see here.

Monitor (BenQ V2220H): the only component I had transferred from the Mac setup. It's an old TN-panel 1080p monitor: not flashy, but it does the job. Not planning to go 4k anytime soon: if anything, upgrading to a cheap ultrawide might be an option sooner rater than later.

Keyboard/Mouse (Logitech G413/G102): there I just went with a familiar name. Being new to the mechanical keyboard market, I figured Logitech have been making great PC peripherals for my entire life, and so far I'm completely satisfied with both.

No RGB or fancy customization/cable management. I'm not willing to spend extra money purely on looks.

Total cost: back in November 2017, the initial build cost me around 50000 RUB (or roughly $850). Since then I've replaced the hard drive and SSD, added a Wi-Fi card, a USB expansion card and an optical drive (BD reader, CD/DVD writer), which might bring the total cost to just over $1000. You could definitely build a better system for that kind of money, but I live in Russia (where all PC hardware is super expensive compared to the US) and I willingly sacrificed present-day performance in favor of upgradability (like getting an overkill CPU compared to the rest of the system, since it's the hardest component to replace).

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In line for upgrades: definitely the GPU (I'm probably going to wait at least another year before jumping to a more mid-range option), monitor (I wanted an ultrawide for a long time).