Instant potatoes are more expensive than real ones? I thought they were cheaper. Guess it depends on the type of potatoes you like.
Seriously, the relative cost depends upon where you are.
Unprocessed potatoes are largely water with some unusable peel. If you've shopping somewhere near where potatoes are grown then the cost of shipping the water and peel to you is so small as to make them cost much less than the instant ones.
But if you live somewhere, say 1,000 miles away from the nearest potato field, then the instant spuds cost about 2/3s LESS than the unprocessed ones.