Best place to buy O2 sensor

I've noticed a drop in fuel economy and my exhaust isn't smalling right so I figure that at 128K the Taco could probably use a new O2 sensor. From what I've read you only need to replace the first of the two sensors and that a bad O2 won't necessarily set off the check engine light.

Where is a good place to buy a good O2 sensor at a reasonable price?

[redtoy92]

http://www.urdusa.com/index.php?cPat...5f83fecc746f7d