Let's talk Total Costs of Ownership of One Laptop Per Child. Taking our set of different OLPC implementation cost calculators, as well as actual numbers that have bubbled up over the years, like IADB's Project HA-T1093 with 13,200 students plus 500 teachers (with a budget of USD $5.1M), we can try to settle on some generalities so we can compare apples to apples.
Common Basic Assumptions
Let's start with how long the project will run, and what number of laptops we'll need to replace (due to age, damage, loss, hardware failure, and so on) during that time frame. That should be easy, right?
Five seems to be the magic number when talking TCOs, which is convenient when projected OLPC lifespans are also five years. Reality may disagree with that (and certainly GeSCI and Vital Wave wisely do).
So let's plan for five years, and drop re-purchasing of the whole batch within that period (see below for why this becomes relevant). We'll instead presume some per-year replacements (damage, theft, environmental problems, and "normal" wear-and-tear), but even this gets harrowing.
Different Lifespan Calculations
The OLPC Deployment Guide handily provides numbers for expected monthly repair frequencies, which they project at .083% risk of bricking per laptop per month - 1% failure over the course of a year.