We run specific components of our application in spot instances across different regions and from what I have seen in the last 3 months is that the price is generally much less than 80%. I'd say is less than 20% most of the time, but some times there is a peak and it goes beyond 150% for 1 to 3 hours, the frequency of these events may vary but I'd say once a week.

I think AWS might be cheaper in this regard but less predictable, so it is a tradeoff.

Edit: I haven't looked yet into "Spot Fleets".