Its all very well saying you can't give a price for an EICR because of all the variables, but this would apply to all trades people in all trades, what is needed is a guide line on an EICR with caveats on additional work, this would allow the customer to have an idea if they are being ripped off or hiring Eddy Murphy.
I think ignorance on the part of homeowners is the problem here. Gas safe certificates are done and dusted in well under 1 hour so they think the electrics are the same
When I talk to people I ask about the size of the house, how many fuseboards, how many circuits, outbuildings. Access to loft , etc etc.
Last year I did an EICR, not because I was the cheapest, but because I was the only spark to ask lots of questions before suggesting a rough price