lossofreeophobia
loss-o-free-o-phobia: The irrational fear of passing up an offer of free goods or services, regardless of whether you need or desire said goods or services.
Fred drove 10 miles out of his way so that he could redeem a coupon for a free car wash, even though his car was already clean and the weather forecast was predicting rain. He has a severe case of lossofreeophobia.