how hard would it be for a avg joe to replace and where could i get a replacment one for cheap

 

1) Read the stickies on the replacement procedure.
2) There is a group deal right now - check that forum. Typically a sensor will run you about 120-140 bucks - check either jrnissanparts.com or courtesyparts.com.

 

On ebay i have seen them as low as 60 bux in the box.
Here is a buy it now for $97.Knock Sensor Ebay

 

alright man to take the sensor out it took me no longer than 3 minutes. all you need is a couple of extencions and 2 swivel joints. you can get a ks of off ebay for liek 80 bucks . since i dont have time to shop around cuz of school i just put in a 470kohm resistor where the sensor is posed to be and the car works fine.