If I pick a instance type that has a current spot price of 0.0067 hr (looks like .0067 is stable for the last 3 months) and the on demand price is .067 hr. When I request the spot instance and specify that I can accept a max spot price of 0.0167. What is the likelihood that instance will stay running for the full month?
Simply best to not play this game. Spot instances are really for specific, temporary, load handling situations..