I heard that it costs Dyson around £24 to make a cleaner
Yes, but this was the same figure that was bounced aroundf before, and it remained unconfirmed as to whether this included all the overheads of running the entire business or not. Added to that, we don't know what Dyson sells the cleaners for.
And add to that, when we talk about the cost of "a few spare parts that cost them hardly anything to produce", it's not producing the parts which costs the money, it's the transportation of them, the storage, the postage to the customer, and -whilst the contact centre remains in the UK- the huge cost of administration. The staff who work in the customer service team costs Dyson a LOT of money and to take this discussion down to it's most simple terms, if Dyson cleaners never required attention in the way they do now, the entire team could be whittled down to about two.