from my experience, it costs way way too much
our first child minder said that after 2 months of looking after 3 kids, she was still better of not working as the costs were SO high in the case of car insurance so she quit
have you considered applying for minicab insurance? covers basicly the same thing but not too sure how hard it is to get nowadays, 20 years ago any old tom dick or dojj oculd walk into a place and get insured for third party fire and theft plus cabbing for £30 a rolling month but i'm sure it's more difficult now