I made up a splitter lead and put a 10k and a 1k resistors as a 'Tee', then a 3.5mm plug. This reduces the audio down nicely for a 'mic' in. Cost was less than a fiver. I use a £17 action camera from a well-known auction web site. I removed the built-in mic from the PCB and put a 3.5mm socket in the case with leads to the PCB mic input. Again, less than a fiver. The video quality is pretty poor but I use this soundtrack in conjunction with higher quality video from a GoPro when editing. The whole cost of the audio setup including the camera was less than the GoPro lead.
TOO