I'm still trying to figure out how tomato cages thrive on the market. For me, the problem with them is simple math: You can't use a 3' cage to support a 7' plant. In fact, every other tomato support I've seen on the market looks just as rickety, and ALL are grossly overpriced.
So in the hope of saving you all some serious dough, I'll share my method which has worked great over the last several years. It's referred to as the Florida Weave.
In my garden, I start with 8' t-posts that I picked up at Tractor Supply for about $6 each. Once you drive them into the ground, they end up about 6 1/2' high, which is good for tomatoes and other climbers like pole beans (another veggie that will quickly outgrow a shorter trellis). And unlike those spindly wood stakes, or even good 2x2 stakes I'd made out of redwood a couple years back, these metal t-posts should last decades. I also LOVE the notches in them, which is ideal for the next step in the process.
This link provides a good description of what a Florda Weave is. Here's how it looks in my garden. I space my stakes 4' apart which allows me to put two tomato plants between them. Then as the tomatoes grow, I weave twine around the stakes creating a cage of sorts.
The twine wraps on both sides of the tomato. The idea is to keep the plant between the strings, tucking the branches over them as they grow.
No matter how big your tomatoes get, this method is surprisingly strong. Granted, I'm one of those gardeners who trims the suckers off her plants. I don't let them go wild, as they end up taking too much space. But usually half way through the year, I say to hell with it, let them grow rampant, and this twine will hold them up well, provided the stakes are driven securely in the ground.
You'll also see in these photos that I've laid down paper mulch around the base of the plants. That's to prevent "splash up" of dirt onto the tomato plant. Soil borne fungus can bring black spot and blight, which I had a small problem with last year. So I'm taking more protective measures this year to keep any dirt off my plants.
So there you have it. The "perfect" way to stake and tend to growing tomatoes, in my humble opinion.