$4 is a little much but there will be sales. The $4 is to get the impatient's extra money. I agree with your general thought process as I also don't need or want every last costume for characters I'll barely play.
I think a lot of people are complaining because they do want every last costume but aren't OCD enough to pull the trigger at that price. But you have to pay $4 for each one, individually, because there are people out there who will play full price for all of them.
They will go on sale when Capcom figures they got the money of those people already.