Track cover for the day will be around £90, so not cheap. Its fine to accept the risk of pranging your own motor, take it easy etc, but what happens if you hit someone else who also has no cover? will you end up paying out your own pocket?? I have done a number of events (when I had free cover), and the tracks can get pretty busy and hairy, I went on a few Hot Hatch events which were populated by yoofs who nick a car the night before and for £30 can kill it on the track with no regard for anyone else. Equally i have done a few invitational events where you get guys with Ferrari and Porsche who drive like complete loons and will take silly risks with their car and anyone elses who gets in the way. Quality of car does not equate to quality of driving. You will have great fun on the track, like previous posters say, its hard to do damage with large run out areas etc, but theres always the chance of you hitting someone or someone hitting you. Maybe safer to take insurance the first time out.
