I'm with Keith Michaels (broker but my actual insurer is Liverpool Victoria I think) who charge £50-60 per track day and £75 per trackday outside of the UK.
I only went with them as I struggled to find insurance last year but now I've changed cars I'm going to try CCI as they offer 5 track days free per year I think. But saying that, I've found Keith Michaels very very good. I speak to the same person every time (Jeremy) and they don't charge for changes on the policy (modifications, numberplate etc) and aren't too fussed on modifications unless they alter the power a fair bit.