The imitable Heather Morrison, in a just-released-study updating David Solomon and Bo-Christer Björk’s 2010 APC paper:
The average APC reported by Solomon & Björk was 906 USD; the average in 2019 for the 739 journals for which we have APC data for both years is 1,363 USD. This represents a 50% price increase during this time frame, an increase that is 3 times the inflation rate.
The cost of processing articles has increased 50% in the last nine years. Right?