Maybe you meant to say this, but what you really need to know is the cost of the rare unplanned tech stop versus the cost of carrying the extra fuel which would have prevented that rare tech stop, except that it's carried on every other flight that didn't need it. My company (A320s and B757s) did such an analysis and an unplanned tech stop costs an average of approximately $8,000 USD, while carrying 10 minutes of extra fuel on every flight costs in the hundreds of thousands of dollars per year. You'd need to do alot of tech stops to justify that extra cost.