Given how many passengers you can get into one lift I would have thought the cost of employing a tech would compare well to the cost of re-booking them.

I honestly have no idea of the costs involved so I guess £300/day to employ a technician. Lets say you have 3 technicians in every day, that's £900 per day or £6300 per week. A lift full of pax would almost certainly have tickets costing more than that so even if you only have one breakdown per week it's a good deal. Which is of course assuming that the costs of re-booking passengers isn't massively lower than the price the passengers paid in the first place. Or indeed that making suppositions based on numbers plucked out of the air is in anyway a solid foundation for one's argument.