A person so obsessed with special offers that it becomes a mental illness causing them buy things they don't want just because they're on special offer.
Often they buy so many things on offer that they have to give much of it away to friends and family.
"My dad is the world's biggest spoffer! Once in a shop he tried on this jacket and knew it was too small for him but bought it anyway simply because it was less than half price."
A special offer. An amalgamation of the words special and offer.
Two beers for the price of one? What a spoffer!