Strange gaps in teleprompter pricing
Like many products, teleprompters vary in price for a number of reasons. First, it helps to understand how a prompter works. A beam splitter, basically a two way mirror, is positioned between the camera lens and the speaker. It allows the light from the scene to reach the camera while the reflection of the display device, positioned below the beam splitter, is seen by the speaker.

In no particular order, some of the factors that influence the price are:


The quality of the beam splitter. Higher quality glass means less light loss to the camera.
The size of the beam splitter. Bigger glass equals bigger text.
The mounting system. How do the glass, camera, and display all attach to each other. Is it flimsy and the speaker will see the text bounce around with the slightest movement of the system? Will a light breeze shake the camera?
The display device. Do you have to supply your own tablet? Is it a high quality display to connect to a computer?
Software. Is prompter software included or do you need to supply your own?
Accessories. Tally and cue lights, confidence/feedback monitors, playback controllers are all options for various situations.