Seconding this. X200/210/220 are dirt cheap, come with modern CPUs, cooling fans (!), quality Ethernet ports and run x86-64 containers unmodified. You can cram 16GB of RAM and SATA SSDs into an X220.
Please don't use the X220 or T420 for servers though.. They're the go-to main laptops for many Thinkpad fans because they're so inexpensive and very well-built for everyday use. There are only so many left. I can't imagine using another laptop besides my T420, I'm not sure a better laptop exists and I'm gonna have to take it to my grave if Lenovo doesn't get their act together and release another Thinkpad with a full keyboard.
That being said, good computers going to good people for them is always a good thing no matter the use case.
T430 is fine too, its my daily driver and has the same charger as the T420.
I run SmartOS on another t430 with a cracked screen which has a bunch of guest KVM and zones. Runs ZFS in a mirror and 16G ram, backed by an APC unit for the modem router.
Where the hell is a X200 is similarly priced to a RPi?!
In my neck o the woods(Austria) a X200 series is around 150-200 Euros. Add 16GB of Ram and an SSD an you're looking at at least 250 Euros instead of just 40 for a PI.
Ha. My home server for a very long time was a RPi 3B+. Totally fine for all kinds of background home server-y tasks, including running a local jupyter server for one-off calculations. (When I need a lot of cpu for something, I probably need a beefy gpu, which is a whole other beast.)
Power supply: It's USB powered. For a home server, I find it convenient to plug it into a USB port on the router, to which it is also connected for ethernet.
SDCard: It was set up to only use the sdcard to boot and use a USB stick as root, which gets around all of the sdcard issues. This is not a totally plug-and-play experience, though. My understanding is that the newer firmwares finally allow direct boot from USB, though.
Case: You can DIY it easily. The case for my home server was basically a folded piece of cardstock on which I drew a picture of a once-bitten pear. Other times I've used legos or dremel tooled altoid tins.
Heat sink: Unnecessary prior to the Pi4. (which also ramped up the cpu and power usage quite a bit...) They keep producing the older models, so it's mainly a matter of picking where you want to live on the compute vs heat management scale.
Heatsink and case were totally optional in my experience (or a case would make thermals worse).
Power supply maybe, if your phone charger did not already work. SD Card or flashdrive; I have many of these lying around.
There is something to be said for having keyboard, pointing device and screen included with a used laptop, but the stuff you list it seems you just don't actually need.
Curious what workloads you're intending to run on the RPI that you find the CPU is tiny.
Granted, the RPi2 had a slow CPU, but I am finding the RPi4 is snappy enough for "serve a website out of a docker container" workloads. I am hitting SD card I/O limits faster than I hit CPU limits.
Much less hassle and similar price to an RPi.