I used American Collector's insurance co. for my 1958 Jaguar XK150. They asked for pictures of the car and we agreed on a fair market value without any appraisal necessary. Of course, the higher you go, the more your insurance premiums will be, so they really shouldn't give you too much of a hard time on an agreed value. They deal with classics and customs so they know that book values don't mean a damned thing. Of course, there were mileage limitations and a requirement that it be stored inside a garage, etc.
Also, despite my very high agreed upon value, the policy was quite inexpensive, costing much less than liability + comprehensive on my daily driver.