Does extended mean more or less than three months?
Are you looking for cancellation and travel interruption insurance of just medical evacuation and/or medical?
www.insuremytrip.com is a great site to compare different policies. We have been using CSA for a while; they have always been reasonably priced and have paid off on a couple of small claims on last two cruises in a timely manner.
I just found out, though, that my TA is able to get cheaper "group" rates at CSA than are available on insuremytrip.com. So, check with your TA after you have done initial research.
BTW, if you are under 75 and are just looking at medical evacuation, I would recommend a policy with medjet.
"Carpe diem quam minimum credula postero"
Seven Seas Explorer - Miami - Venice - Mar 2017
Silverseas Explorer - Arctic - Aug 2017
Seven Seas Voyager - Rome to Beijing - Oct 2017
Seven Seas Mariner - Lima to Buenos Aires - Jan 2018
Silverseas Explorer - Siberia - Jul 2018
Seven Seas Mariner - Australia Circumnavigation - Dec 2018