From the header file of a standard Project Gutenberg etext (in this case that of the Rubaiyat of Omar Khayam (tr. Edward Fitzgerald):
We produce about two million dollars for each hour we work. The fifty hours is one conservative estimate for how long it we take to get any etext selected, entered, proofread, edited, copyright searched and analyzed, the copyright letters written, etc. This projected audience is one hundred million readers. If our value per text is nominally estimated at one dollar then we produce $4 million dollars per hour this year as we release some eight text files per month: thus upping our productivity from $2 million.