2001 Nissan Altima Question: how much should it cost to replace both oxygen sensors and how hard is it. How d

its as easy as changing spark plugs, you can get the special socket from harbor freight for around $5 or get a loaner from advance or auto zone, the socket has a split in it so you can put it on (passing thru) the o2 sensor wire, you can spray the sensor with some pb blaster to aid removal, sometimes its best to tighten a little before undoing, it helps it break free. Its very easy, but on some cars access can be a little difficult, but by using extension bars etc it can be done. Ive done mine on the vw passat twice front and rear.