fuel sending unit??

so i got a 94 nissan pathfinder with real real real real real real low mileage(218k) and it needs a fuel sending unit…where is this located and how much would one of these cost…and how hard is it to replace???

in the tank attached…not hard to replace if u have very little gas…i dunno if pathdfinders have the fuel access panel in the floor like Maximas…i woudl assume they dont…so u gotta yank the tank