Used Lenovo Tiny M92p/M93p units make a nicer solution for this, to me. The enclosure is already there, and no janky USB storage to deal with.
If you really want to compare a 200$ desktop with a 40$ SoC then you should aim for stuff such as those mini PC's/thin clients from Asus, which nowadays even ship with Ryzen processors.
And a used Lenovo Tiny is easy to find for much less than $200. $100 shipped without an SSD, $140 with one.
You're exaggerating both ends.
Parts from Ali:
Stackable plastic frame for 4 pis + basic heatsinks ~= 5$
MicroUSB PoE injector (removes the need for PSU) ~= 3.5$
That's true, but we can break cost down easily. Right now there are RPi4 packs with power supply, enclosure, and both passive and active coolers for less than 15$. Storage depends on your taste, but you can buy 64GB USB pen drives or micro SD cards for less than 10$, or 1TB external HDD for less than 50$. Thus for a total less than 100$ you can have a brand new server up and running.
I'm talking about stuff you can simply add to your shopping cart and get it shipped to your doorstep in a few days with zero research. These prices were literally taken from the first search result that popped into amazon.
Better yet, this option involves zero time wasted betting on whether end-of-life hardware still has a few months left in them.
There's no way you can do much on the rPi4 without active cooling - mine gets uncomfortable hot doing some basic web scraping, never mind server duties.
You'd be surprised. YMMV and of course your local climate and your usage patterns do dictate how hot your gear runs, but in my experience adding a small 1$ heat spreader does allow my RPi4 to chug along without going over 60C. Heck, even placing it on the side or placing a coin stack over the processor is enough to keep it running along without ever throttling.
Of course if you're constantly running 100% CPU loads then you start to need cooling, whether it's your laptop or desktop or even servers.
This one is sold out and out of production now though and I had to trim it because it was made for the 3+
It also uses much more power, most of ivy/sandy bridge low power desktop generally idles at more or less 15W, where the RPI 4 uses less than 4 watts.