This describes the potential for making an inkjet machine. Even conceptually, inkjet machines are complex in principle, so much so that I suspect it drove the makers to jump quickly to the development of colour printers. Meaning, so much effort needed that the next step was worth exploiting quickly.
But that leaves the possibility of simpler single colour printing worth exploring, I should think. Making a prototype machine, slow, or even handheld, does not appear to be a path filled with hidden pitfalls.
Some thoughts:
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The printer head. This would be a cheap laser pointer. Work is needed to discover whether a more complicated lens is needed, in order to focus the light to the paper in sufficient intensity to char it. Once that is achieved, the amount of time to keep the light switched on needs to be controlled.
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The placement. A second laser pointer, placed perpendicularly to the first, coupled with a light sensing diode, can ‘read’ the x-y coordinates of the operating pointer relative to a piece of paper placed in a tray with mirrors at each corner. This is a simple computation.
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The ‘pen’ holder. This actually doesn’t need a major guidance system. Rather, the image file, translated as a bitmap, can be used to confirm that the pen has moved over all the points where a black point is needed on the paper. The holder is then a fairly simple jig that holds the pointer perpendicular to the page, and it can be lightly ‘scratched’ all around, pretty much randomly, to create the final image on the paper. An additional visual counter connected to the bitmap reader can inform the user what percentage of the image has been completed, or a full-screen display can describe visually what parts are omitted or incomplete. Of course, for pages of text, the user will herself know whether the print quality is acceptably readable, even when not fully printed.
I suspect that even if an RPi is dedicated to this tool, the total cost will be within Rs 5k, not counting the time and effort of the prototype maker, of course. But if the RPi is just being cycled through different jobs, then the overall cost will drop to a few hundred, max. I don’t know if an Arduino will be even cheaper.