That seems to be drastically understating the change.

The M4 Mac mini was announced two years ago with 16GB RAM standard, starting at MSRP of $599, without anything like an education discount (which knocked another $100 off the machine), and stayed at that price until early this year when supply simply evaporated. Then the M6 model this fall went up by $300 for the same base memory and storage capacities. +50% in overall price of the entry-level machine, and probably not much of it was due to the M6 being a more advanced processor than M4.