[ Photography ] Open Question : Cheap External Mic for Canon 7d?

I have a Canon 7D and usually only do photography, I've come across a client with a small instructional video project and I'm looking for a cheap external mic for the project. Most of the video is actual footage of product being applied, but I do need to do a few short interview sections and I'm worried about the quality of the sound from the camera's mic. I don't have a lot of experience with actual video production and this sound doesn't have to be superior quality, but I am looking for something a little better. Any suggestions?