There is detailed discussion on this here:
If you will participate in 7-10 HPDEs a year, WSIB will sell you an annual policy. Kraig Hopkins is the director of that program there.
Underwriter is Hiscox, a syndicate at Lloyd's.
For 1-10 HPDE events per year (events with multiple days still count as a single event), the premium is 3.5% of the agreed upon value. For 10-15 HPDE events, it is 4.0%.
Events that involve timed activities are NOT covered, but they have a special product that covers racing and time trials. That supposed to be more expensive though, but I don't have much info on that.
I heard that there are a few companies that sell liability coverage on the track, but I think that is also meant for racing.