It cost about $50.
here's the tech sheet:-
Flush mountable inductive proximity sensors
Cylindrical M5 form A case in metal
PNP output
2m cable or M8 plug-in connector
LED for visual indication of output state and short-circuit protection
technical specification
Rated supply voltage 5-24V d.c.
Switching capacity 100mA
Maximum switching frequency 5000Hz
Operating temperature -25°C to + 70°C
Degree of protection IP67
