It is surprinsigly hard to move paper the way a printer does it. The easiest way for DIY would be to use a continuous roll of paper and a very thin pen on a 3d printer like stepper motor, like older dot matrix printers.

If it fits the quality you need, I think a plotter is actually the best option; the FOSS ones seem to just take arbitrary pens for ink and there's a fair few projects implementing open source plotters that seem to get decent results.

Printer hardware is very specific, so you don't have generic versions of everything, defacto standards and official/unofficial documentation like you do in other DIY-able fields like 3D printers and CNC. The best you can do is buy replacements or salvaged parts for existing {HP,Canon,Epson} printers and spend months reverse engineering them. This will not only cost you more than buying a very nice new printer, but will suffer from the same availability issues every project depending on parts that aren't regularly for sale.