I think they are building into their calculations discounted prices, based on the fact that many owners will choose to go for the low cost version, when available
They are quite adamant that they are loking for a low cost product of between £500 and £1000, although there is no sign there is a manufacturer willing and able to do it for that sort of price
I've written to my MP on this and the chair of the Transport Select Committee, as I feel this is open to review. They already acknowledge uncertainty in costs, but still want to implement, and are bodging the figures to suit