As with most things I am not a price buyer.
The company I use, TCP thru Firemans Fund, specializes in professional photographers. They insure my gear including computers. When I rent equipment I add it to my insured list by e-mail and it is insured as of that e-mail.
If I need a liability insurance endorsement for a permit or a studio rental, I send them an e-mail and it gets faxed out the same day. And they know the permit requirements and endorsement requirments for most of the major jursisdictions.
I have had friends who have had anything from small claims to very large claims with them and to a person they have been treated extremely well and in one case, above and beyond to get equipment covered that missed being on the list (thru oversight by the insured) and to get the claim paid quickly.
What does it cost? Well not much different than what you might pay with a homeowners policy or elsewhere. But I must tell you that I don't worry about how I might be treated if I have a claim or if I need something taken care of.
Anyway they are at
http://groupinsure.com like I mentioned before. And they are also a provider thru one or more of the asscoaitions, ASMP or PPA or ?. I just don't remember which one, I am a member of all of them.