What's the purpose of a Matte Box? The big flags help shade the lens from flares or any little bit of light adding better color and contrast, and also allows placement of certain filters such as ND, Gradients, and Polarizers. With filters you would be able to control shutter drag, aperture, color, and other details. Nothing beats the real thing, but if you can't afford it, there's some clever DIY tutorials out there. YouTube member EquippedforMedia puts together a DIY Matte Box starting with a tray for a weighing scale. Filter holder is the popular Cokin P series, which i've used myself in Hawaii.
The Cokin Filter system is a light weight cheap filter kit (mostly plastic), but great for traveling and keeping things light. With a good Gradient ND Filter you can bring down the bright sky while still maintaining proper exposure on the landscape. Keep in mind these filters are not just for video, but enhance your Photography too. One thing to keep in mind that as you stack filters in front of the lens, it's harder to manage with Wide Angle Lenses.
So instead of going the DIY route to control Lens flare, Cokin already has a square hood with filter holder to get you started with a Matte Box type look, and filter holder functionality. They are also stackable so that you can make the hood longer or shorter. What you'll need to make this happen is the Filter Ring (choose correct size), Filter Holder, Square Hood (or several), and P Series Filters. You could probably score all of this for under $30 bucks.