Add title in front of 'price'

You will have to edit the file "listing_price" of the view "product" via the menu Display->Views.
There you can easily get the groups of the user via that line of code on Joomla 2.5:
$userGroups = JAccess::getGroupsByUser($user_id, true);

For Joomla 1.5, you can use that code:
$user =& JFactory::getUser();

if($user->gid==XX){
echo "text1";
}else{
echo "text2";
}

XXX is the id of the user group. You could put it at the beginning, after the first <?php tag for example.