I certainly feel the need to apologize to my students for the
absurdly high value of the k in Coulomb's law. Two one-Coulomb
charges, separated by a meter, exert a force on each other of
nine billion newtons, nearly the weight of a cubic football
field of water!
To try to justify such a choice, I promise them that we'll later
see that this sets the size of all electrical units, and although
the Coulomb is inconveniently large, the *volt* turns out to be
just the right size for things like batteries and chemistry.
As for the *exact* value of k (or epsilon_0), I don't try to explain
that until we get to magnetic forces between wires.