The OrangePi zero is a small and affordable SBC. Advertised as a $ 5,= singleboard computer, but it to get it will set you back a little more: Including shipping € 10,= (so twice the price mentioned).
The board as build in Wifi, an ethernet port and one usb port (and a micro usb port for power). In the past other OrangePI’s uses another powerplug, which was not very smart. This one uses the expected micro usb plug. There is a pin header for audio/video, but I never used it. There is also a GPIO header (32 pins) but you have to solder this yourself.