I was just shopping for insurance about a month ago and found a wide range of rates for my Challenger T/A with an agreed value of $75K. The quotes ranged from a bit over $300 to over $700 at Hagerty. Grundy was almost as expensive as Hagerty. Heacock was a little under $500. And I finally talked to a broker, Rally Insurance in Volo IL, who specialize in classic car insurance, and they found me the $300 rate. I believe the name of the company is Classic Insurance. I have the info at home and can check later.
I used to have all my vintage cars through State Farm, but have been concerned about their "stated value" vs agreed value. I brushed my concerns under the rug for a while, but recently got my T/A back from the restoration shop and needed to up the value to what it is worth now. I'd need an appraisal for State Farm to up the value, and for the hassle and expense of getting an appraiser out to the house, it was time to go with a specialized classic car insurer. They will typically agree to a value based on photographs and a description.
I still have my convertible and my '71 Challenger with State Farm in their classic policies and both are under $300 a year with one a little over 50K and the other a little under 50K in stated value.
You must have your daily drivers insured with State Farm to insure cars under their classic car insurance though.