Countries like India and Brazil have shown that you can successfully run payments infrastructure nationally. Turns out it's not all that difficult or expensive or at all. India's NPCI processes 500m transactions daily with an annual budget of about 50m dollars. They make a profit over that while keeping the system free for a majority of users.
[1] https://www.indiatoday.in/business/story/npci-rs-500-crore-p...