At the moment BT Retail's Infinity FTTC VDSL2 product appears to be about the cheapest on offer but yes I'd not fancy BT Retail being my ISP either.
Hopefully over time as the wholesale VDSL2 service becomes more widespread it'll become wires only meaning no engineer visit to your house will be required which should mean the price will come down as happeed with ADSL but alas thats a few years away I fear.
Not sure how much BT Wholesale are charging ISPs for VDSL2 circuits but either Retail are absorbing some of the cost or other ISPs are charging more to cover the cost of necessary upgrades to their networks or a bit more margin as it's still largely in early adopter stage.
Virgin (ADSL) => Namesco => Newnet => O2 => Plusnet => Zen => Newnet => Zen Lite 8000
Note: I don't lay turf for anyone. astro or otherwise, all views and opinions expressed are my own based on experience.