Citing the (how to put this politely?) languid economy, Walmart.com cut prices on its pre-order DVDs down to $10. With free shipping. And not just on the Criterion Blu-Ray Release of “Cool Runnings.” All the summer’s big hits-“Angels & Demons,” “Terminator: Salvation” and “Julie & Julia” are all available for bargain bin prices. Target and Amazon quickly followed suit and added titles like “Harry Potter,” “Night at the Museum 2” and “Star Trek” to the list. Be advised, however, because Variety is reporting this pricing is only available online and only until the movies are officially released on DVD. But you don’t know that because you have already left this site, haven’t you?