I've signed up for or seen the contracts for several payment processors across several companies. Rack rate for ACH debit starts at $0.25/trx and goes down to sub-penny at scale. Returns can be high though ($2 per, going down as well).
Edited to add: that's not a defense, I *loathe* ACH. It's a negative-reporting system which is such a pain to deal with.
What I can say is the Fed has draconian rules for pricing its services. The services cannot be subsidized but must be priced to recover costs, including a return on capital similar to what a private payment system (ie from the Clearinghouse) would expect.
I read it as the sending institution pays 5.2 cents to the receiving institution per item, on top of the 0.35c/item + 0.1c/item same-day surcharge for a maximum of 5.65 cents/item before volume discounts.