If you're in the market for 3-D video projectors, you have a lot to choose from. What makes 3-D devices different is that they can project what looks like two images overlaid with a slight offset. You'll need to wear the 3-D glasses that come with the projector to perceive the two images as one three-dimensional picture. We've covered this technology in more detail in our article How 3-D TV Works.When selecting a 3-D video projector, you'll first choose between these different types:As of this writing, HD 3-D projectors range in price from $850 to $6500. The PC 3-D-ready projectors fell in the same range, but included some cheaper models around $300. No matter which type you choose, the projector's up-front cost and maintenance is higher when you decide to go 3-D. Here are some of the costs you should expect besides the projector itself:Sometimes you need portability in a projector. On the next page, we'll check out what makes video projectors portable, and how you should shop differently when you have portability in mind.