I'm still waiting for someone to try out this 4 lens monster mentioned by @Arjun !
It's not cheap and it's not small. I see sites listing it for $1,400 or so but Andy said he could ship it for under $700. (..but wife said that is not happening for me. )
I'm not sure how you would be able to usefully view it though.
It produces a long panorama blend of the 4 cameras. I don't think it has an option to connect to each of the 4 camera feeds individually.
So trying to watch it on a monitor, much less my BI phone app may not work well or at all I imagine.
It would be really cool though to have one camera image to monitor a whole yard overview in one image.