Funnily, enough, my charger installation was completed only this morning (5th July).
We appeared to need an isolator board / box (I don’t know the details) and initially thought we were going to be charged for this, but don’t seem to have been.
Also, it seems popular around these parts to give BP Pulse (who either fit themselves, or subcontract the work) a fair bit of flack for being hard to work with, difficult to contact, useless etc, but in my personal case it was as straightforward and smooth as I could envisage.
I did the BP Pulse survey which did take a fair while (lots of info, a dozen pics or so), once submitted I was contacted within a week with a fitting date, which itself was within a week, so under 2 weeks from getting the survey link to actually having a working charger ready to juice up the car when it arrives.
Anyway, as far as extras are concerned you MIGHT need an isolator which should be inexpensive, and if you have a ridiculously long cable run ( > 15 metres?) then they’ll charge a bit extra for that. You certainly should not be looking at a huge amount but afraid I can’t tell you if it’d be above or below 3 figures.