I suspect that you'll see (say) £1500 quoted irrespective of whether you put in a group of 2 people or 200 people. Then, fairly obviously (unless the insurer really won't pay out more than £7.50 per person for the larger group!), the figure quoted must be 'per person', rather than for the group as a whole.
You can probably save yourself a lot of searching anyway by simply going to the sites recommended on MoneySavingExpert. My own travel insurance (12 months, multi-trip, Europe-wide cover for a 64yo guy) cost me just £16:
http://www.moneysavingexpert.com/insurance/cheap-travel-insurance
(I've got the most basic package with HolidaySafe but there are other policies available:
http://www.holidaysafe.co.uk/ )