Have to agree with you.
Think about it from their perspective. A couple "kids" under 21 want to pay you money to cover all the possible costs of repairs for a car worth $200k? Due to their age, they likely dont have a lot of driving experience, more along the lines of you CAN'T have a lot of experience due to your limited time at being able to have a license. Plus young drivers are more prone to speeding, etc even if you personally don't fit that category.
How much money would charge a couple of people that came to you, asking you to take on that risk? I wouldn't be surprised if they asked for $20k just to insure you if anyone actually agrees.
On the other note. Best of luck mate. Would be awesome if you actually got it covered.