Film a 3D video using Genlock cameras or LANC?
Genlock would allow the capture of frames to be synchronized to a common external timecode.  It is only a feature on pretty high end cameras, so if you are trying to keep costs down, it really isn't an option.  The other question I linked to in the comment goes over a few possible ways to try to get usable sync for multiple cameras, but sadly, there aren't particularly good options for most cases.

There is a 3d kit for certain model GoPros that may be worth considering, but otherwise, you are probably best looking for a camera that supports lens splitting for 3d capture or purpose built consumer targeted cameras if you want things to remain fairly cheap.