The NY Subway alone handles approximately 1.7 billion riders a year, and the MTA system as a whole sees roughly 2.6 billion riders a year. For a 18.5 billion annual budget, that breaks down to only $7/rider/year.
For those in other countries wondering why so many US citizens always seem adverse to the expansion of government services, it's because they can't perform basic arithmetic.
The entire London Transport system runs on a ~12.7 billion dollar budget with over 4 billion riders a year, which comes out to a cost per head of a bit over $3, and yet last time I checked their transport system seems to work just fine. Trying to imply the MTA is underfunded won't work here.
Citation needed. Per wikipedia and the sources linked there, the London Tube only sees 1.4 billion riders a year, and has a budget of approximately 12 billion pounds (or roughly 15.6 billion USD), for a per-dollar approximate cost of roughly $11.14/rider/year.
It seems like MTA manages to do more with less. If you just want to compare subways (NYC vs LU), the numbers still favor the MTA.
So yeah, implying that the MTA is underfunded works just fine. In fact, based on the experience the LU has been having, I'd argue that the LU is also underfunded for its ridership and that both systems could use more support.
The London Transport budget report for 2018/2019[0].
The 4 billion is total ridership over all London transport services, equivalent to the 2 billion number you used for all MTA services. If you just wanted to talk about the subway you should have used the numbers for that in the grandparent
