Try calling my agent, he's the owner of Farmers Insurance group here in San Diego but he could cover your M5 there with no problem whatsoever.
Dave Ellison at (619) 293-7503 and don't forget to mention the password, "Adrian sent you" then he will give you the Adrian special discount...
I'm 32 and my premium for full coverage with 250 comprehensive/500 collision deductible plus $50 car rental coverage is $85/month (for my M5).
Give it a try and you'll be glad you did.
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Adrian
01 M5 LeMans Blue/Silverstone - Titanium Trim