old/damaged laptop + basic wood working skills + monitor = all-in-one pc
can even make a mini pc depends on the motherboard pcb
what you need is a laptop that's basically functional, it needs to turn on and work when plugged in, don't care about battery, keyboard, trackpad, screen or caseing
now depends on the internal board but most or only about 33% of the laptop size, and that's pretty much all you want.
Often ports are on sub-boards connected via ribbon cable so they can be repositioned and layed to bring down the foot print.
now build a box to put it in.
connect monitor via hdmi/vga, keyboard and mouse via usb, and power via the charger
1mini pc, might be longer but should be flatter.
need more usb? build in a usb hub
build it onto the back on a monitor, all-in-one pc