How did the Catholic Church function logistically/liturgically prior to the invention of the printing press? During a Catholic Mass, there are a great amount of readings and prayers and scripture extracts/arrangements. There are different reading and set of prayers for almost every day of the year. This applies to both the Novus Ordo and the older, Tridentine Mass, as well as to various liturgies that existed before that too.

I've noticed that a lot of parts gets read by the priest from liturgical books (I think the most important one is called a Missal) during the mass.

This has got me wondering, how did the church function liturgically for the first 1600 years before the printing press? As I understand it, books were insanely and prohibitively expensive to produce back in the day. I seriously doubt that your average parish in the countryside of the British Isles could afford a handwritten missal. But that leads me to wonder, how did the average parish cope?

Readings from the bible and set prayers from the missal are absolutely essential to the liturgy. There is way too much there for a priest to memorise it all, so what did they do if they had to say mass but didn't have access to a bible or missal for the readings and prayers?

Or maybe I'm underestimating the Church and in actual fact your average countryside parish did have access to all the liturgical books, in which case my question is instead, how did they afford it?
From Herbert Thurston's Catholic Encyclopedia article "Missal" (§ "Origin of the Missal"):


  The printed Missal of the present day, reproducing in substance the manuscript forms of the latter part of the Middle Ages, has resulted from the amalgamation of a number of separate service books. In the early centuries, owing to the lack of competent scribes, the scarcity of writing materials, and various other causes, economy had greatly to be studied in the production of books. The book used by the priest at the altar for the prayers of the Mass usually contained no more than it belonged to him to say. It was known commonly as a "Sacramentary" (Sacramentarium) because all its contents centred round the great act of the consecration of the sacrifice. On the other hand those portions of the service which, like the Introit and the Gradual, the Offertory and the Communion, were rendered by the choir, were inscribed in a separate book, the "Antiphonarium Missae" or "Graduale" (q.v.). So again the passages to be read to the people by the deacons or rectors in the ambo (pulpit) — the Epistle and Gospel, with lessons from the Old Testament on particular occasions — were collected in the "Epistolarium" or "Apostolus", the "Evangeliarium", and other lectionaries. Besides this an "Ordo" or "Directorium" (q.v.) was required to determine the proper service. Only by a slow process of development were the contents of the sacramentary, the gradual, the various lectionaries, and the "Ordo" amalgamated so that all that was needed for the celebration of Mass was to be found within the covers of one volume. …


Medieval Books of the Hours (and illuminated manuscripts in general) were common, especially among the wealthy laity, before the printing press.

See also the "Manuscript" Catholic Encyclopedia article for the history of manuscripts and copyists.