OP switch is 0.35$ per unit, but only if you by 5000 ... and it has the problems 6by9 mentioned.
Compute model 3 does cost 35$ in Germany, with two Csi2 interfaces.
Pi camera multiplexer 6by9 pointed to does even cost 50$.
Two Pi Zero have two Csi2 interfaces as well, for 2*5$=10$ (or 20$ incl. shipping).
--> Raspberry camera / gstreamer / raspivid / raspiraw (bookmark list):
https://github.com/Hermann-SW/raspiraw https://github.com/Hermann-SW/userland https://twitter.com/HermannSW