I just wanted to pass along a source for o2 sensors I recently found. You can buy OEM Ford o2 sensors for $70 (front and rear) or $50 (fronts only) I have recently started purchasing from this individual and was extremely impressed by both quality and speed of shipping, especially since they are coming from Canada.
Below is the link from Corral.net classifieds:
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Definitely an excellent value from a conscience seller
Hope this is benefitial
Tim (Musttanguy) PonyPerformance.com