I just got my insurance on my 182, I only had to pay a extra 24.99 to drive any other car on a 3rd party basis.
I am 20 with 3 years NCB.
This is with BELL insurance on their flexibell policy.
Whilst on the phone i asked if my brother was able to take a similar policy when he needed to renew and they said aslong as he is on a flexibell policiy that is fully comp, he can take the option to drive other cars ( he is only 18)
Hope this helps
/bazz