Analog sensor signal isolation for ADC/DAQ
Given you have no 

1) accuracy requirements, 

2) no dynamic range requirements

3) no linearity requirements

I'd just use the sensor output to drive an LED; if you have linearity needs or want to avoid the deadband of an LED, then use a voltage-to-converter circuit to drive the LED.

Then couple the photons to a photodiode into a TIA at the DAQ.

Certainly less than $10.

Or just use heavy copper braid to tie the DAQ gnd to the sensor gnd. Much cheaper.