That's the hammer! You can get a good motor for one of these for not much more than £30, and there is a special rod and control box that fits to the cabinet so you use the treadle plate as the motor control; this leaves the work invisible and means you only have one very unobtrusive power cord that won't get in the way. You might have to wait a while for one of these to come along, but they do pop up. The other option is to buy a wrecked one and use the bits you need from it.
You'll be very pleasantly surprised how well the treadle works though; most who have them wouldn't swap to electric. Enjoy your machine