What type of bike are you riding? Something super exotic?
I've done many, many track days and raced all sorts of bikes and never had insurance on them. I've crashed race bikes a few times, but never on a trackday. Ultimately, I think if you ride within your limits with a well organized group, and take care of other riders (particularly beginners), then you can keep the risk pretty low. And it you're not riding something exotic, I'm sure you'll find the potential cost of repair * risk factor < the premium.
However, you NEED good health cover and/or loss of work cover. That's the important piece. Don't go out there knowing that if you injure yourself, then you could be down six figures in lost income and hospital bills.