I'm expecting 7.5p at home per kWh, Octopus though offer some interesting deals, with sometimes 50% off if you charge that night, but don't charge the next day! 
Gixer is telling me he is paying 7p, I think that is Octopus
Maybe half of it would be motorway, I'm wiggling my way from Camberley to Woking, then to M25. So should be able to get some regen in on that kind of run.
I don't think you'll see much range benefit of regen. In an ideal world, you could turn that off and coast and probably save more, but its all down to other traffic and driving styles.
Motorway speeds do eat power on EVs, more dramatically than ICE cars. Trouble is, until you actually get one, you simply won't know how well it works for you. Personally, I'm not prepared to piss around with public charge points, even ignoring the costs involved. Others are more willing to take a break in their journey. Which is why we are at a point, with our usage, where EVs keep disappearing off our list of potential replacement cars for her XE.
Sky is not bad for charging support. 66 spaces here at the HQ across 3 car parks. You can book them ahead, which has a perk of also booking a parking space
The building I'm in has 6 parking spaces for the building, our company has 4500 people there across about 10 floors, a government agency has several floors in same building. You have to be a special spacca to be able to use one of those 6.
And, as its in Birmingham, you can't use public carparks. So I have to tolerate the crap entity known as Chiltern. Which reminds me, I have another compo claim to pop in, as my choo choo to London was 'dangle berries'ed by a signalling fault at Wembley.