oxygen sensors

hey guys im getting up towards 100K miles and was thinking it would be a good time to get some new o2 sensors. I was just wondering do the 2000 mustangs have 2 o2 sensors or 4 o2 sensors. Also, does anyone have any websites that i could get them for under $60 each, cause thats the price at autozone, advance, oriellys, etc etc thanks for the help guys