> If there's a marginal cost for each copy of the data that's transferred to a user, I don't think asking the user to cover that cost conflicts with a requirement to "give away the data".

Charging the user for data, even if it is on a marginal cost basis, conflicts with a mandate to give data away freely. Because “at the marginal cost of delivery” is not “free”.

(It's true that it is common for mandates to specify something like at marginal cost of delivery rather than free—sunshine laws providing copies of public records often work that way—but that's not the applicable mandate here; in fact, since without the separate mandate here the data would be available on a marginal cost basis under FOIA, the main reason for a separate mandate is to negate that cost.)