2000 Buick Lesabre O2 sensor

Hi... I have a 2000 Buick LeSabre Limited with appx 114000. My "Service Engine Soon" light came on a couple of weeks ago. I took it to AutoZone and had them run a diagnostic test. I was told one of the O2 sensors needs replaced. I've noticed in the past two days that while driving from a stopped position (such as at a red light) that when I start to drive I can feel the car slightly kick while it goes through the gears. Is that one of the signs of an O2 sensor needing replaced? Also what is the approximate cost of a repair such as this (I'm a single female and don't want to be taken advantage of when going to have the repair done). AutoZone rep told me $75.00 to $100.00? Thanks, Melissa Short