DerianCypher said:How large would a city have to be in order to support some sort of educational institution?
What would the cost of attending an institution be?
DC
Sorry "the chump" ran out of steam (and soy milk... he went through the whole gallon....

Incase you were wanting this information for a campaign you're running, here you go.
Historically medieval education was for the rich or the religious. Aristocracy (nobility, gentry included) would have private tutors, or they would be sent to another noble's household to learn from them (following them around and learning from observing/doing)
Religious medieval learning was mainly for reading, reciting, and copying scriptures. Of course if you were from a aristocratic background and went into religion as a profession, there may be more extensive learning.
There are universities in medieval times.... but most of the time, the students rotated around the professors, who usually travelled from place to place teaching. Very different than what moderns think of when we hear "university"
From MMSWE chapter 3 (I included libraries for you as well)
Libraries
Magical medieval libraries are private libraries where people
can enter for a price. Most libraries are not owned by a single
person, but by groups. Books cannot be taken from the library,
and librarians can always refuse service. Libraries often require
people to use a guide or a librarian to expedite searches, as
well as to prevent theft and damage to the books. These
assistants are, of course, also compensated in coin. Because
of magic, other restrictions are in place in some libraries.
Libraries may require complete disrobing of their patrons.
These patrons receive official library robes and must purchase
their pen and papers from the libraries’ personal stores. Even
stranger measures may ensure the security of the collection.
There are many different types of libraries in magical medieval
societies. Medical, legal, magical, civic, scholastic, and
religious libraries all offer different benefits for its users. Stored
knowledge is the main benefit provided by libraries. This is
especially useful for knowledge checks because having access
to a relevant library adds a circumstance bonus. Libraries also
house small scholarly social groups, allowing them interaction
with other like-minded groups. Libraries are another form of
public display through architecture. Built of stone and
elaborately decorated and carved, a magical medieval library
can be as grand as any cathedral.
Universities
Magical medieval universities are centers of learning, and
attending university is usually a step towards a profession.
Medicine, science, history and law are common professions
that spring from university attendance. Wizards, with their
dedication to research and learning, have a natural propensity
to found universities to further learning. Students pay
professors at the end of class, and their pay is a measure of
the professor’s performance in the classroom. The university
is a community between teachers and their students. Not unlike
craftsmen of the same guild, they drink together, talk together,
socialize together, and celebrate together. Generally, magical
medieval universities are private endeavors of affluent
organizations and citizens.
As for how large of a community is required for such structures, that's a hard question. Generally, at least a small or large city in 3E terms, but I'm tempted to say, maybe even a metropolis. There can be educational institutions in smaller communities (like some monastic orders in the historic medieval era).
As for cost of attending such an institution, I have no idea... so I guess you stumped me too

Check out our free preview (http://www.rpgnow.com/product_info.php?products_id=693) which will tell you which wards are likely the seat of universities (if you have one in your city) and other useful information about generating medieval urban spaces.
Happy gaming,
suzi