Similar issues happen for justifying security. But if you've got a price tag, then just do expected utility. What's the odds that you'll need a backup? 1%? 0.1%

Similar issues happen for justifying security. But if you've got a price tag, then just do expected utility. What's the odds that you'll need a backup? 1%? 0.1%? Per year? And what's the value of that backup price tag during that time? $10m? 0.1% per year * 10m = 10k per year.