There is an excellent piece by FactCheck on the Channel 4 website here. FactCheck investigated the claims by the No2AV campaign that the cost of a Yes result in May will run well over £100m due to need to introduce electronic voting machines, as counting ballots manually under AV would be too difficult.
FactCheck find that:
They find the NO2AV’s claims are ‘fiction’
There’s never been any suggestion that electronic voting machines will be necessary under AV. Australia has used AV for 90 years has never had electronic voting, all counting is done manually.
As such there’s no estimate of how much it would cost as it’s simply not necessary and therefore not on the cards.
Furthermore, in elections in Northern Ireland and other countries where they use STV, a more complicated system, counting ballots is still done manually.