How much money are you willing to spend per nine? How many nines do you need? Do you replicate across 3 or more data-centers? What about across 3 or more continents using 3 or more providers?
If you're running a heart-transplant registry, you probably need 10 nines, if you're running a cat dating site, you probably need less. Sure everyone wants massive uptime, but few are willing (or even need) to take the steps needed.