Question: I want to assemble several cameras, triggered by a single remote. Is this possible?
The trigger doesn't have to be wireless, because the cameras will be very near to each other. The cameras need to be very cheap, because I'll be needing 50 of them.

Answer: 
This is the product recommended by Chris Breeze and Eric Pare at Xangle amongst others - the Esper Triggerbox <https://www.esperhq.com/product/triggerbox/>

The ESPER TriggerBox is the world’s leading programmable multi-camera shutter release controller. Up to 6 cameras can be connected to each TriggerBox and it allows multiple camera to be fired simultaneously or with programmed sequences and offsets + multiple TriggerBoxes can be linked together to synchronise larger multiple camera setups and they neatly stack together, a bit like LEGO bricks! [![enter image description here](https://i.stack.imgur.com/YFFtf.jpg)](https://i.stack.imgur.com/YFFtf.jpg)
It can be done with GoPro cameras, and the [GoPro wifi remote](http://shop.gopro.com/accessories/smart-remote/ARMTE-002.html). You can pair one remote to multiple cameras, apparently you can control up to 50 cameras at once. See [Controlling Multiple Cameras with One Wi-Fi Remote](http://gopro.com/support/articles/controlling-individual-cameras-with-the-wi-fi-remote-when-multiple-cameras-are-paired)

Though it wouldn't be cheap, if you need to buy 50 of them. The cheapest current model would be the Hero3 White edition, which has wifi built in. Or you could use an older HD Hero or HD Hero 2 with the wifi bacpac, but these are now discontinued and getting harder to find.

This video is a nice example of using 52 GoPro cameras for a "bullet time" effect. <https://www.youtube.com/watch?v=zKtAuflyc5w>