Yes so you need government funding to get the chargers in the first place otherwise it doesn't make commercial sense. Not sure that covers everything but lets say it does.
Average Supercharger cost per kWh in the UK is say 67p/kWh
Cost per kWh to supply the site is maybe around 26p/kWh x 20% VAT so let's say 31p/kWh
Ignoring any other costs of running the network (Obviously there is) then they make 36p/kWh
Average speed of charging is maybe 100KW so in an hour it can make £36
Let's say it's in use for 8 hours a day, other hours it's empty so that's £288 a day from a single Supercharger or £105,120 a year
Say we have an 8 stall site then £840,960 a year
Average speed of 50KW and that halves that number, in use for 4 hours a day on all tombstones over 8, halved again. Maybe doesn't start to stack up by that point. The costs to run the network are unknown but you imagine the bigger the scale, the cheaper that'll become.