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Have you had a look at subsidies etc? I'm attending a "cargo bike showcase" in Hammersmith on Friday to promote take up of cargo bikes. The council are pushing a scheme by an organisation called MP Smarter travel that offer up to £2k off the purchase of a cargo bike. Might be worth looking in to if you haven't already, whichever bike you decide to go for.
Also, it looks like Paradise Cycles have the Bullitt X in stock for £3,099.
Would be for business usage, but 6k, whilst not surprising, is somewhat off putting.