I am not sure if this is helpful, but I created a spreadsheet for comparing different electricity tariffs. >
LINK<
You can enter details from a typical (pre EV purchase) monthly bill, e.g. monthly day and night usage, night time schedule and day/night KWh costs. Then put in your typical weekly car mileage for each day of the week (Only change the green and yellow cells, otherwise you will break the calcs).
The spreadsheet will estimate how much that mileage will cost you (it assumes you do as much charging as possible on your night tariff and then overflows to the day tariff only when you can't get the charging done during the night time schedule).
If you want to look at a different supplier, just make a copy of one of the sheets and then change the details (the summary page is done manually, but you should be able to add the new supplier with basic excel knowledge.
It isn't perfect (because it has to make some assumptions about your example month usage), but it isn't bad as an estimate.