Rock Auto is just using generic terminology, as it is application dependent. It is refered to as the water inlet because the water enters the engine throught this inlet. It exits throught the passenger side (outlet). Technically speaking, the water flows in and out of both the engine and the radiator.
A new water inlet from Nissan (the pt. # I listed) should probably cost ~$45 depending on the source.
Yes, the '00 Sentra will have the same part as well. So, 2000/2001 Sentra w/ RR motor, and 2000-2002 G20 w/ RR motor.
I see that you also mentioned the Thermostat housing in your thread title. Do you need the T-stat housing as well? Keep in mind that the VE and the RR T-stat housing are different part numbers. I am not sure if the RR T-stat housing (on the back side) will bolt up to the VE water pipe.
So, the VE/RR inlets are the same - 13049-2J200
However..
The VE and RR T-stat housings are different part numbers:
VE - 11061-2J211
RR - 11061-2J201
Maybe buying an entire used VE thermostat assembly (housing and inlet) off of the forum would be a cheaper idea. Then, you could just pop in a new t-stat and be set.