It costs us maybe $700 a year to have comprehensive cover on a vehicle insured for $10k (with an excess of maybe $1500 or something). I figure if we have an accident on average every 15 years, then that’s $10,500 when the payout would be $8,500 after excess.

Now I mention it, before you go for third party, see what your excess is. You can often save quite a bit by moving that up to $2k or even $5k (depending on the value if your car).