My response which is qualified below would be Raspberry PI Zero (W if you want WIFI) V1.3 and a Raspberry PI Camera V2.1 via CSI-2.
I recommend MotionEyeOS if you want an quick/easy method of getting streaming working.I'm comfortable compiling up motion with mal_ driver support but I recognise thats not everybody's cup of tea.
IMHO this represents the most cost effective hardware and a decent quality camera.
I have three headless Raspberry PI Zero (1.3) with CSI connected Raspberry PI Cameras V2.1. I use them to stream at 30fps. They all run the stock 32Bit Raspberry PI OS.
I use motion application on the RPI)'s but have turned off motion detection so its just used for streaming. This is because there is no way a RPI0 can do motion detection at 30fps however it can stream as long as your network bandwidth is up to the task.
I have configured the RPI0 as Ethernet USB-Gadgets which means they are powered and use the networking over a single Micro-USB cable to a single hub which also acts as a router and homebridge server which means I can access the cameras from any Apple device. iPhone, iPad, Apple TV etc.
The hub also runs motion and it does the motion detection on the 3 cameras and is setup to do movement alerts via homebridge.