This project is really great! I started looking into the build process and the cost. This could be achieved at a lower cost than $10 plus shipping.

Using a guide, like this: http://www.instructables.com/id/USB-foot-controllerlooper/
You could use an old usb keyboard or a new $4 keyboard with a box and some buttons. With two buttons, you could directly type i and esc without having a background service running.