You may not know this website since your new, but CourtesyParts is a dealer in Texas ( maybe even close to you im not sure, check their location ) they offer in store pickup so you can save on shipping, but alot of people on here use it for OEM parts.
Since there really arent to many aftermarket options for the r50, and im sure you just want a OEM replacement, they have it for $133.
Heres a link to the part, you can see in the table your pathfinder specs as per what you put in your profile here - 2001 2WD 3.5L, it is listed in the 5th row from the top if you are paranoid about it being the wrong part or something.
http://www.courtesyparts.com/56230-rear ... _4800_4804&
EDIT: Also to be 100% sure, the bar you are talking about is the one that runs in FRONT of the rear axle if you are looking at the truck from behind, and also that it is not one of the swaybar links holding the swaybar, there is 1 on each side. Taking into account your sway bar is broken, im assuming it was due to something extreme happening, either offroad or a huge pothole or whatever from the previous owner, i would also change the sway bar links while your at it, and the bushings.
For those things i would recommend going to advance auto and ask them for MOOG rear sway bar links, and bushings. There are a total of 2 bushings for the sway bar. MOOG's are an aftermarket replacement to the OEM but they are a bit better, and also they have grease zerk fittings on them so you can use a grease gun to prolong the life of the mini "ball joints" that hold the sway bar.