I looked at the power supply cross reference list on this site and it was all 1606 series power supplies. No mention of a 1756-PAxx or other PLC power supply anywhere.

The cost of the power supply far exceeds the cost of the backplane. What gives? Are there any less expensive sources than good old alphabet-octagon?

Used / Surplus, like from www.plccenter.com/ at least these come with a one year warranty