I am not sure if this will help as you are the other side of the border.
Here is BC our basic car insurance is controlled by the Provincial Gov't, it does however allow you to seek private insurance in as much it relates to collision and comprehensive coverage. They also offer a collector and modified collector program, that has defined perimeters which provides a much cheaper rate compared to a everyday driver. Currently any car/truck built prior to 1991 is eligible for this program but strict guidelines for interior, exterior suspension and performance modifications have to be addressed to qualify. They however, do not have an agreed value clause in the policy. They rely on market value from what I understand so it does allow for much comfort for many. You also have to be a registered owner of another car/truck to qualify.
In my case and because I have modified my 2002 I have chose a third party provider to address my needs on the recommendation of the shop that painted my car. I was required by the underwriter to have an independent registered appraisal completed before the Insurance company was prepared to enter into an agreed value clause. It covers 100% if anything happens to the car with the exception of PL & PD coverage. It includes storage insurance when ever the car is not licensed for the street. This forces me to buy basic insurance but at a much cheaper rate than the general public, ( because of the collector status).
As far as the premium is concerned I think each state or province is different so dollar figures will likely not mean much. I can tell you that in my case my combined costs for basic and agreed value is more than half of what I would pay for basic coverage with a relatively low deductible with NO agreed value.
Finally most of the guys around here do use Hagerty as their third party insurer, I do not. Also I am not sure of their requirements but I understand they place a value on the car based on their research and pictures, no appraisal required as I understand it. I think their premiums are fairly close but I am sure in my case the premium is likely higher based on agreed value.
I am sure you will get lots of response that will be better suited than mine...good luck!