We came across some great instructions for crafting your very own custom screen hood over at the DIY Photography blog. If you're careful with a saw and superglue, you can get a result that looks professional with minimalistic stylings.
Plastic sheets like the one used in the tutorial can be had for $7 to $8 from your local hardware or home store. Add in the cost of a strip or two of Velcro, and you're coming in at under $10.
It's not just the cost savings that makes this a worthwhile project. By tackling this the DIY way, you're guaranteed to get a privacy hood that fits your monitor (even a laptop screen) without any extra bulk, and in the exact color you'd like. They make plastic sheet in every color of the rainbow. Hit up the full post at DIY Photography for a step-by-step tutorial on getting it done.