I offer an SQL book as a free download. It is very popular. In fact it
is at #1 position on a Google search for "SQL book". On the download
page, there is a checkbox to check if the person is interested in
receiving a "database tips" newsletter. I have a list of about 70,000
people who are interested in receiving the newsletter. The list grows
by about 5,000 each month.

My intention was to create and edit the newsletter myself but now, I
find I do not have the time to do it justice. I would like to partner
with either a publishing company or a large software company to do
this.

My question is this: If I want to be hands off and act merely as an
editor, how do I arrive at a value (in monetary terms) for this list,
bearing in mind the newsletters potential to accept ads in the case of
a media company and the potential to market database products in the
case of a software company?

In the answer, I'm looking for a methodology to follow to arrive at
the valuation rather than just a figure.