Paul, one of the cheapest would be a pistol case. I've bought them for $10.00-$15.00 at gun shops and some of the big discount chains have them. Another little more expensive case is one by Case Guard [they make rifle and pistol hard cases] called the 'accessory case', both are big enough to be used for two TX's if you want but you have to cut the foam to fit your TX. My opinion these are much better than the cheap aluminum tool cases that you can buy at Home Depot-type stores.
Fred