The major argument I've seen for that cost being "outrageous" is that if it needs to cost $2.50/month, there should have been a greater-than-30-days warning so

The major argument I've seen for that cost being "outrageous" is that if it needs to cost $2.50/month, there should have been a greater-than-30-days warning so that the existing clients could shift business models to support it (shut down free access, migrate existing subscribers to plans that cover the cost, etc). It's the failure to provide a grace period that gives the impression they're just trying to shut down the third-party clients. For reference here, the Apollo dev posted numbers indicating that they'd expect a $20 million / year API access bill, and separately mentioned that if everyone with a current annual subscription gets their balance refunded now they're shutting down it'll cost them ~$250,000. (It's hard to guess how much of their traffic comes from free users, of course, so they'd presumably need to raise prices less than the 40x this implies...)