I own a very large, and very successful web hosting company with over
100,000 customers. I am interested in selling my business. Is there a
formula (and I know it won't be exact) for how much to ask if I want
to sell my business?

Figure out the amount of money the website is actually making per
month gross (do not exaggerate); now multiply this amount by 2 and
again by 6 (months). This is the high value of the website. Now take
take the amount of money that the website is making per month net and
multiply by 6, this is the low side. Don't accept any lower than this,
you may accept more than your high amount as this only gives you an
idea of what to hold out for (somewhere in the middle, usually).

Really if I was you I wouldn't sell the website for the simple reason
you'll make much more money over time than if you were to sell it.
Also remember that this formula is just based on my knowledge of the
subject, if you do choose to use it you are aware that you are doing
so on your own free will; don't blame any losses on me.

Howdy cds-ga,

As the former ISP owner/operator (that I sold) I have specific knowledge
of your type of situation, and can add to it with current information from
the internet.   However, you might want to consider your Question's pricing
as $2 will not even begin to cover the work involved in a proper answer to
your question.

Looking Forward, denco-ga - Google Answers Researcher