I went to Best Buy looking for a DVI <-> HDMI cable once. They wanted 40 dollars. I got it on Amazon for 7.95. And they wonder why their stock recently took a big hit...
I second this. Monoprice is great. Their cables are dirt cheap yet at least as high quality as what you'll get anywhere else.
They're also great for adapters. I bet 10% of the people reading this have paid Apple $30 for a Mini DisplayPort to {VGA|DVI|HDMI} adapter. I got all 3 for $30-something.
Yeah I had to pay this much just recently. I was annoyed as I knew the same item would be avaialble for roughly $10. But I needed it that day - not an option to wait a couple of days for delivery when you have no display.