I can sort of understand the build costs going up if they've been digging holes and realised that it's costing a lot more than they anticipated, but I really don't understand the monthly rental costs going up almost three fold, and an extra 50% on the connecting part of the charge.
There's a fair amount of suspicion that it's related to the new BDUK connection voucher scheme, whereby SME's can get a grant of up to £3000 towards the installation cost. This will likely lead to a lot of demand from SME's and they can justify the increased monthly fees. Openreach likely doesn't mind taking a larger piece of the grant pie each time either.
Openreach didn't see enough demand from individual consumers (though I have to wonder whether the kind of speed freak early adopters who would be interested in this kind of product weren't already tied into FTTC contracts) so they've retargeted the product and adjusted the rental to suit the expected market.