I got a Plantronics 'something' 320, which was $40 here (rip-off land a.k.a. Canada). You should be able to score a Voyager 520/620/whatever for less than $50, which I hear is pretty good.
Honestly, if it's just for use in a car, anything that pairs with your phone should work. No need to filter out background noise or whatnot, which is actually incredibly useful. So if you can afford it, just get a Jawbone and be done with it. Maybe your wife will like it enough to use it 24/7 and avoid the brain cancers.
Just be careful, cheap headsets indeed suck at filtering out noise, and make it difficult for the person on the receiving end to hear if theres any significant background noise; in a car that would be radio/open windows/fans/ricer engine.