Almost every teaching environment (not just classrooms) has a document camera. The Minneapolis district went with Lumens. It has a flexible "goose neck" that is easy to position where you need it. It also has an LED light that is also flexible. This does help with image quality. The other nice tool is a remote. Lastly, it can be connected to your computer and has the software to be able to run it through the computer.
I specifically mention the ability to run it through your computer. It's a huge selling point. You can put student work under the document camera, click "capture" and save the image to your desktop. I've done this with artwork, written pieces and even 3D creations. I worked with our art specialist to take pictures of 20"x30" drawings for a presentation. We put the art on the floor, snapped a picture and then put it into the slide show. Very cool feature.
There are other great features. I've stopped making copies of handouts because I can put the original under the document camera and have the students use their own paper for answers. This cuts my valuable prep time, saves copy time and money, and saves expensive copy paper.
We also do a lot of thinking (mind) maps. Students can present their map to the class using the camera. At the same time, I can take a picture for grading and give the original back to the student.
This also works great for meetings. Put the hand out under the camera. This way you don't need to run copies for everyone who is going to throw it away.
If you issue is cost, don't consider it. If it is used correctly and consistently and teaching practices change, it will save money and time in the long run.
The only issue that we've had at our school is goose necks that lose their hold. This is solved by pulling it straight and then curving it again.
I'll leave you with a quote from a good experienced (older) teaching friend:
"This is going to change teaching. I can find a sample of a leave on a class walk, bring it into class, put it in under the document camera and the whole class can see the whole specimen in full color. With overhead projectors, they would see the dark outline. Imagine what I could do with dissections!"image credit: picturephone.com