If your site goes down, you lose money. From a simple power outage to a cracker attack, if you go down, you're covered. Insure it for that amount. Liability Copyright infringement can cost you big. Companies are insured anywhere from one to 250 million.
Premiums are heavy.
Prices can start around 5 grand and go up from there. Other insurance companies have jumped on the bandwagon and have started offering Web-business insurance. It's nothing I can afford personally, but I can see a major corporation needing it. I would think that two years ago, people would have been much more tolerant of a computer crashing. Your server is expected to work.