Hello, how are you doing?
I am interested in your project, I find it quite original :)
I could accomplish what you need, but using Adobe Premiere, which I find to be better than iMovie. This shouldn't make a difference for you if you want just the final file and not the editing file.
My actual rate would depend on the number of videos. How much are you willing to pay per video?
Contact me back if you are interested!
My best wishes :)