Service Engine Soon flashing on 2001 Nissan Altima?

Service Engine soon light flashing on my Nissan Altime 2001 ran 93K. I went to AutoZone and found error codes P0141 and P0325. How much it will cost to replace oxyzen bank1 1 sensor2 and knock sensor . Is there anyway to get rid of these error codes from OBD as I have emission test due for August'11.