Recent APC price changes for 4 publishers (BMC, Hindawi, PLOS, and PeerJ)

Following is a summary of recent APC changes for 4 publishers, prepared on request but posted in case this might be of interest to anyone else. In brief, each publisher appears to be following a different pricing strategy ranging from flat pricing over many years with one rare exception, to a tenfold increase from 2016 – 2017.