I'm not sure track day insurance is worth it. It's expensive and they usually have a very high excess anyway so if something does happen you still have to shell out quite a bit. Add that to possible maintenance costs (oil, tires and other little things) and it can be an expensive day out. If you go to a well organised track day you won't have to worry. You are not racing at a track day (I'm not even sure they time you), so just allow faster cars past and keep a good distance from other cars. Track days are more just to allow you to drive your car on a track within your comfort zone and your own pace. People are generally very well behaved and won't race you or put you in a situation of danger. There are marshals there as well to make sure everyone is having a good safe time. I did a day at Oulton park and was worried about insurance but I was getting silly quotes so said screw it and went for it. It was an absolute blast and at no point did I come close to having an accident. Just be sensible and you'll be fine. Most people there are in the same boat driving much more expensive cars.