Here are two options. I've used On-Track because they have a lower deductible ($1500 instead of $3000) and their rates are about 30% less than Lockton's. I've found the prices to be more around $200 for a single day event with $35,000 coverage. MVP Track Time has an affiliation with Lockton. Fortunately I've never had to call and file a claim so I can't make any comparisons in that respect.
HPDE Insurance Program
hpde insurance, race track insurance, de insurance, track driving school insurance, on track insurance - ontrackinsurance.com