To be honest I don't like "The game is for children" argument either. I think it's more likely targeting young adults. Games are no longer just played by children.
While I don't like how NTR acts, it's true that the price for a costume isn't that bad if you don't plan to collect all of them. It really is money you can spend if you enjoy the game. I mean, making that costume does take effort so it has its price. What I personally dislike are how expensive the consumables are. Those are just a picture plus some code. Compared to what it takes to implement them the price is like printing money....