I've noticed in a lot of anime series that the episodes are sold in silly spans. Sometimes, 4-5 episodes are sold at a silly price. Why are volumes grouped together like this? It can't be good for sales.
In short, They sell them for that much because that's how they've determined that they will make the most money.
the net marginal cost of producing the CDs is high Sometimes they don't expect to sell very many copies of the dvd in the first place, and they have to sell them at a higher price to cover the overhead. The more dvds that they produce and sell, the lower the net marginal cost of producing them.
People who do want to buy the dvds will pay that much for them Sometimes the fanbase is strong enough and small enough such that those who will buy the dvds will pay any amount for them, and the number of people who would pay $20 for the dvd, but not $50, is relatively low. in this case, it makes sense to sell the dvd for $50.