Melinda, before you run a low hot wire, it will be trouble if it is kept low. Try running a strand of barbed about 2 inches from the ground, pull it banjo string tight and then tie your fieild wire to it between the fence posts. They will not crawl under that. It will also help to keep the less desirable creatures from crawling under from the outside.
Yup, cattle panels will work and, you are right, they will be expensive.
Don't get me wrong, I am not downplaying the low hot wire. It is just a problem being low that it will be more prone to shorting out because of wet grass and weeds making contact with it.