I know that a couple of guys have had problems with crank shaft sensors. If you notice here: http://www.alldata.com/TSB/06/98067733.html
Even on my car, they had a recall on my car. Maybe if they had a recall on your model, the dealer may cover the cost of the replacement.
I used to drive a Jeep with a 4.0L inline 6. Its crank sensor failed about 47 miles from the nearest town... About 20F degrees outside, and no cell signal. Oh and 3 am. Greatest night ever! Yeah and the operator fell asleep on me when I called the operator, so I called again... Anyway I did finally get a tow truck driver at 4am. He said he would be right out. He finally came about 6:00am. I waited for 9 hours for them to get the part. And $250 later, I found out that autozone had the same part for $20!
I would get it fixed. The crank sensor doesn't give much warning when it goes out.