remote cameras streaming to ATEM switchers

What is the cheapest ATEM unit that can use RTMP inputs? If I'm reading the website, it looks as if I'd have to get Blackmagic Design ATEM Television Studio HD8. And can I stream in non-Black Magic cameras that allow for a custom RTMP server?
Thanks.

IM not sure .. But i think, u can stream to ATEM only from BMD cameras ..

For rtmp streaming Im using WOWZA server .. Camera is streaming RTMP to it .. And im using Raspberry PI ($30) as a decoder for HDMI output to ATEM ..