Multiple step-down of DC voltage in one circuit
Although Andy Aka's solution is probably cheaper, four SN65HVS880 may also do the job.


  The SN65HVS880 is a 24-V, eight-channel, digital-input serializer for high-channel density digital input modules of PC and PLC based systems in industrial automation. In combination with galvanic isolators the device completes the interface between the 24-V sensor outputs of the field-side and the low-voltage controller inputs at the control-side.