Does Sunba produce WiFi camera?

The answer is, not yet. And we currently don’t plant to develop a wireless outdoor camera due to concerns primarily over connectivity and user experiences. Chances remain that we will develop wireless models for indoor cameras as well as low-zoom in mini PTZ.

IP Cameras, compared to analog cameras, may have lags in image transmission as they are very dependent on the local network. In case of wireless, problems such as stability and connectivity may happen, especially for high zoom IP cameras. Wireless plans should work better for smaller and fixed lens cameras.

PoE is usually considered a great alternative for wireless cameras because for wireless cameras, you still have to run a power cable  (one cable solution). For PoE cameras, it is the same one cable solution but instead of the power cable, you need to use ethernet cable.

If there isn’t any forms of running a network cable, you can consider using wireless bridge to connect the camera.
In short, as you said, you can use a client wireless AP to connect to your root wireless AP:

http://www.hometoys.com/article/2012/09/using-a-wireless-bridge-and-megapixel-ip-camera-for-remote-security/1870/
Wireless bridge is widely used in surveillance projects.