I don't know of any insurance for a tortoise. Have you found a place that would actually insure it? I personally think if it were available, it would be a waist of money.
I originally thought about getting an insurance policy when i got my tort. In the UK you can insure them for between £10-£12 a month. Obviously depending on the type of cover you choose if something does go wrong then you are covered up to £2,500.
Alternatively you could put the money into a seperate account and build up the money in case of emergency. It will take a while to build up the funds but if you never use it, you will have a nice little savings account.
There is a pet insurance place here in Columbus that does tortoises and turtles too, but in my opinion, I wouldn't get a policy. As long as you have a safe, escape proof enclosure, take care of your little guy well, I'm not sure why you'd need one... Just me!
micro chipping g could be handy, though.