I was wondering if it might be possible to "pervert" the technique of screen printing to make a printing head: On Wikipedia there is information that the structure of available screens has a granularity of up to approximately 400 DPI, so I think that would suffice. If we could find a way to create little sqares with only one mesh left open, we would have a cheap device to place ink on many materials. Sure - this is a pretty unconvenient way that probably will be quite slow, but imagine: the printhead would be so cheap, it could be thrown away frequently. Maybe each time paper is refilled or dried color polluted the printhead?
The biggest challenge among developing a way to create such "printing heads" would be fine tuning the squeegees that place an appropriate amount of color on the object. I suggest a little motor is rotating while the hole should be opened when desired.