Earlier quoted context omitted.
It costs about a hundred and fifty grand annually (fully loaded, base salary 80-90k) to have the lowest end person who could conceivably keep one of these things running well for three years. n+1 means you need two of them in case one gets the flu. Tell me again about how Amazon's a ripoff, please.
You're still going to need n+1 sysadmins to maintain the rest of your infrastructure. Maintaining a storage system like this really isn't much different for the day-to-day operations. So, yes, it's one more system, but you're already going to need those admins anyways.
So we're talking about $75,000-90,000 a year in salary to maintaining the cluster if you want 24x365 coverage (which Amazon provides), as you'll need 2 people per shift, 3 shifts per day at a minimum to have people in house, even if they're only spending 10% of their time actually working on that particular issue. In reality, these are unrealistically small numbers. Each employee will have a cost to the corporation of $125,000-150,000 a year. Employees of that caliber spending 10% of their time on supervising a cluster for a year is $75,000-90,000. I'm amortizing the amount of work over your 3 datacenters by imagining you already have the staff and only counting out the number of hours needed for just this work.
So the reality is that you left off something like $225,000-270,000 in actual cost of running your own cluster from your analysis, because while it's not "much different", it is a few hours a week from at least 6 employees if you're really talking about running managed, highly reliable storage.