It wouldn't need to be costly at all. The remote would need to send a command to the device via the USB port. The reader would just need a firmware update to recognize these signals and respond as if the button was pressed. For example, you click the Next Page button on the remote, and a signal is sent to the reader. It recognizes the signal, and turns the page.
I would use a wired remote that plugs into the USB port of the reader.