One of the ironies of book collecting experience is that sometimes the most widely distributed ephemeral material is the most difficult to collect today. This is certainly true of early broadsides and song sheets, which rarely appear on the market. Yet according to the scholarship quoted below, these now exceptionally scarce items were the most widely printed and distributed of early printed material. The first quote discusses the cost of early printed material and the limits on its affordability by the relatively small percentages of society that were literate. The second quote argues that popular short works such as broadsides and small pamphlets were remarkably widely distributed, even if they were not widely preserved.
"What does 'popular' mean? Print was a luxury commodity. Print was not produced by the people; for the most part it was produced by particular interest groups with the people. Even if the compositors and press-operators, the hawkers and street-pedlars who sold small books, and a handful of authors from humble backgrounds—even if these participants in the production of cheap print can be said to come from the people, printing was a capital-intensive business, and few early modern books can be said in this sense to represent a popular voice.
"Print was expensive. A pamphlet or an early newsbook or a chapbook would cost a penny or two. A labourer might earn as much as a shilling for a day's work in the seventeenth century, but the century saw periods of wage stagnation, economic pressures, and rising food prices. Few could realsitcally have afford such an outlay on anything like a regular basis.... Moreover, the most effective form of social exclusion or censorship is mass illiteracy. Around 1500 perhaps about 90 percent of men and 98 per cent of women were illiterate; by 1600 this had fallen to about 70 per cent of men and 90 per cent of women, and by 1700 about 50 percent of men and 70 per cent of women were illiterate. The numbers were proably higher in Wales, Scotland, and Ireland. These are maximum figures, however, and it is likely that forms of rudimentary reading literacy were signifcantly higher. And, of course, there were other ways of accesing the contents of books that did not involve buying or reading them, including religious and political communities where texts were read aloud" (Joad Raymond, Editor, The Oxford History of Popular Print Culture. Volume 1, Cheap Print in Britain and Ireland to 1660  4).
"Strong arguments have been made for both sermons and playbooks as the most popular printed texts in early modern Britain. Yet while sermons and plays were firmly rooted in oral cultural and both were clearly printed and consumed in large numbers, the kinds of printed texts most immediately identified with both orality and popularity...were also those that were the mostly cheaply printed: ballads (single-sheet songs in verse set to music), broadsheets or broadsides (single-sheet texts), pamphlets (small texts usually printed in quarto), and chapbooks (slightly longer longer texts, usually printed in quarto or octavo). Scholars estimate that there were 600,000 to several million ballads circulating in the second half of the sixteenth-century, and while the term pamphlet embraced a wide range of texts—social, political, ecclesiastical, and topical in nature—the format was uniformly affordable (the price for unbound books in 1600 was around a halfpenny a sheet, and small pamphlet or chapbook was within reach of a day labourer.
"According to Margaret Spufford, the publisher Charles Tyus, who had no monopoly on the trade, had 90,000 octavo and quarto chapbooks in 1664, one for every fifteen families. In addition to being cheap, these formats were used for both the circulation of oft-told tales and the introduction of new and topical ones, widely disseminated in London and the other publishing centres, and by itinerant pedlars, throughout Britain; and frequently discussed (and often excoriated) by early modern men and women precisely because of their popularity" (Julie Crawford, "Oral Culture and Popular Print" IN The Oxford History of Popular Print Culture. Volume 1, Cheap Print in britain and Ireland to 1660, Edited by Joad Raymond  114-115).