oxygen sensor

Ford service checked my ford contour 1995 because a bad smell comes from the exhaust. The diagnosis was that the oxygen sensor was working intermittently and should be changed. It seems that the part costs $70 but they and every other mechanic I have asked wanted $400 fro the job. I have two questions: 1) how bed is it to drive the car without fixing it *besides the smell); 2) is it possible to put the new part by my self? and if so where can I find direction of how to?
Thanks

If its the zetec 4 cylinder, its an easy fix by yourself since there is plenty of room to work around. If its the V6, youll still be able to do it assuming to have the right tools. (wrench) Installation is pretty straight forward. Find out which 02 sensor it is, unplug the sensor, unscrew it, screw the new one back in, plug the new one in. Its not hard, but can be time consuming if its the V6 since its cramped for space. I would change it, since youll probably be getting pretty bad gas mileage.

$400? For an O2 sensor? Holy sh!t! I agree with BeyondLoaded, you should definately change it. Its an easy fix, even if you're not the most mechanically gifted. Did they tell you which O2 sensor it was?

thank you all for your ansers. I believe I can do it my self because unscrewing and screwing should not be a problem ugnoring the fact that I don't know what an oxysen sensor looks like. Since this might be a problem, is there any manual that I can use? To your questions, my car is 4 cylinder, and Ford did not tell me which O2 sensor I need

this is what an 02 sensor looks like
http://www.buyautoparts.com/ebay/images/isuzu-02-sensor.jpg

thanks for the information i'll give it a try