Actually, there was a significant industry in major urban centers of mass-producing cheap editions of textbooks before the invention of printing. One lector would read a text aloud while 20 or 30 scribes would make simultaneous transcription, creating 20 or 30 copies of a book over the course of a couple of days. Also, professors often dictated the sections of texts they wished students to study, and thus students would end up with full editions of their textbooks. Even in antiquity, inexpensive books in codex form on technical subjects (medicine, agriculture, rhetoric) and Bibles were available; booksellers, as people in any other business, offered their wares at a variety of different price points, ranging from functional reading copies to more expensive copies. Also, public libraries existed in the Roman Empire, and in schools dating back to Aristotle's Lyceum. People could consult books in libraries for free.
While medieval illustrated manuscripts are one example of book production before writing, they are only one very specialized type of work, and represent only the luxury end of the pre-print book market in one specific culture. Saying that all books were as expensive as as gorgeous Book of Hours illuminated with gold leaf would be like saying that people could not afford clothes before sewing machines because elaborate ball gowns worn by the nobility were very expensive.
The first major instance of the impact that the Renaissance had on our society was the rise of Protestantism. Martin Luther and John Calvin were among the important figures who felt that the Roman Catholic Church had moved away from the roots of Christianity and began abusing its power. Today, many of the Christian churches in the world are descended from those of the Protestant Reformation. The rise of Protestantism also diminished the authority of the Roman Catholic Church and eventually contributed to the separation of state and church, which is now common.
The second major impact the Renaissance had on today's society was the development of experimental science. Much of modern technology and medicine can be traced back to the rise of scientific inquiry in the Renaissance.
In literature, writers of the Renaissance rediscovered classical forms of secular literature. The major Renaissance literary innovations that impacted modern writing include the rise of the vernacular, the beginnings of realistic and mixed-mode drama, the rediscovery of the novel, and the use of the vernacular.
The development of the printing press is, in my opinion, the event that has had the biggest and most lasting impact on today's society. We say that knowledge is power; without the printed word, it is difficult for any society to obtain and to maintain widespread knowledge (although not impossible). The printed word is a tangible, concrete and lasting way to acquire knowledge and to transmit it.
Of course, books existed before the invention of the printing press. However, those were handwritten and richly decorated through a long drawn out, painstaking process, using expensive materials. Because each book was created by hand, each was really a unique work of art. They were created by monks, and were strictly reserved for the very rich or for those religious orders that created or collected them. In other words, they were very rare and used by a select few. In this way, knowledge was restricted to those who could afford it. Of those, few could even read them.
With the printing press, books could be mass produced, using cheaper and more readily available materials. They could be sold to anyone who would pay for them. Through mass production, they could reach more people, thus spreading knowledge to those who would have been excluded from it before. Moreover, since anyone with the skills and equipment could print books, subjects became increasingly varied, and new ideas began to spread, such as philosophy, sciences, and others. As books became more available, literacy increased and an interest in learning followed.
The invention of the printing press was truly revolutionary. We owe much of what we know today to this momentous event.