This seems very backwards to me. The job of business isn't to do the "simple and fair" thing. It's a) to generate maximum value, b) to extract enough cash to pay the bills and then some, and c) work to keep costs at an effective minimum.
The marginal cost of a single API call is approximately zero. Reddit, like most SaaS businesses, is much more about fixed costs than variable costs. I think they are much better off following the standard freemium approach, where they give away what's basically free, and then use value-based pricing to get a fair share of the possible revenues. The sort of cost-based pricing you suggest a) doesn't match their cost model, b) overcharges for valuable things that may not produce direct revenue, and c) undercharges for things that are especially valuable to users.
The marginal cost of a single API call is approximately zero. Reddit, like most SaaS businesses, is much more about fixed costs than variable costs. I think they are much better off following the standard freemium approach, where they give away what's basically free, and then use value-based pricing to get a fair share of the possible revenues. The sort of cost-based pricing you suggest a) doesn't match their cost model, b) overcharges for valuable things that may not produce direct revenue, and c) undercharges for things that are especially valuable to users.