The best stuff to make cages out of in my opinion is the welded wire mesh used for concrete reinforcement. It takes a little time and a good tool to cut it, but the resulting cage is much higher than any of the little prefab units you can buy at the garden center. This height is necessary or the tomatoes will grow out and over very quickly. Any rigid wire fencing that has openings big enough to stick your hand through and pull out a tomato should work well.
One other thing, you will need to keep all of the tomato vines inside the cage. Checking them about every 3-4 days and pushing errant vines back through the cage to the inside should be sufficient. In the rare case where the vines need to be tied I use small strips of old pantyhose (don't laugh, it works great!) If you're gone for a week, the vines will get too long outside of the cage and tying to the cage will be necessary.
One last tip. I clip off the bottom horizontal strand of wire on each cage. This leaves a multitude of 4" long wire "spears" sticking down to anchor the cage to the ground. In areas where wind is a problem, this won't be enough, and additional stakes will be necessary (inexpensive tent stakes, 3 per cage, work great).