The paper he is using is 53 cents per page according to the provided link. Ink cost is a bit harder to determine without knowing how many prints per pen. He is including free shipping, could easily be $5 to $10. There is also the matter of the time taken, the overhead of space and electricity and that doesn't even acknowledge any creativity. I'd estimate the break even point to be around $20-25. Much less than that and it would be more sensible to not bother doing anything at all.
HN never fails to disappoint on the "let's read his comment as the most extreme possible version it could be, nevermind subtlety, nuance, or reading!" front