As it turns out it doesn’t actually cost that much on regular transit, there’s an AIRPORT SURCHARGE because it’s an “airport train”.
No wonder Americans don’t use public transit, even when the system exists it’s ridiculously difficult and expensive to use.
I once went through a BART gate line by mistake, I was trying to get to the trolley service and misread the signage. I immediately exited. The charge: $6.20. Still can’t believe it.
Use cash.