Also, remember that although warfarin (coumadin) is cheaper for the pills, it also requires huge amounts of monitoring. During the start of warfarin your wife will have to go to the anti-coagulation clinic every 4-7 days for them to stabilize her dose. After that every month and only after she is stable for a long time could it be every 3 months. These visits come with their co-pays and deductibles too! Not to mention that warfarin has significant risks, drug interactions, food restrictions etc. And overall: you have to think of the worse case senario of switching to warfarin having the warfarin be too strong and your wife getting a bleed of some kind. This could be in her GI track, brain etc. and can be very life-threatening and could cause huge hospital bills.
So, depending on how long she will have to take the plavix for, and what she is taking it for, it may actually be less expensive to use the plavix.
Plavix and Coumadin have some of the same indications, but they are not interchangeable. Discuss if switching to Coumadin is an option for you.