Look at it this way: suppose someone reserves all the DVDs at a location. This prevents anyone else from getting one.

So, to ensure that people actually want the DVDs they reserve, they need to charge you.

Now, as for the fact that a $1 DVD turned into $30. It sounds like that's due to the fact that, with a debit card, they put a "hold" for $30 to ensure that they'll get paid if the DVD isn't returned. This is a reason not to use a debit card (or a credit card near its limit) with things like this.

This said, $1 DVDs do sound like a cheap form of entertainment. Much better to spend $1 for the entirely family to watch a movie, than $12 for a theater ticker for one person.