The Theracane is basically a cane with some hand-holds, which is meant to make it easier to massage areas like your back. Experimenting in the store, I did not feel it was really suited to deep, high pressure massage, but it would still probably be a useful tool. Check out their website if you haven't seen the Thera cane before. The problem is that it goes for between $50 and $30, usually without any return policy. I've come up with a couple of $1-$5 alternatives which work pretty well.
First, you could always try doing a tennis ball massage, (just trap the ball between the wall and your body, and wiggle around). This works OK, but doesn't really make for a deep massage because the ball is too big. Also it can be difficult to pinpoint the spot you want on your body this way.
So, what I really suggest is to go to a kitchen store (I went to IKEA) and find a short kitchen tool which has a round handle, as in the picture to the right. The one I found cost 99 cents. Now, since it's not rounded on both sides, it may be kind of hard to hold comfortably, especially when applying lots of pressure. Solution: cut open a tennis ball, and stick the non-round part into it. Now, you have a nice soft handle, and a good, hard massage point. For extra force, I put the tennis ball up against the wall, and then lean into the rounded handle of the tool.That works pretty well for the lower back. It's a bit hard to position the tool, since it's all happening behind your back, but your arms can be flexible enough to make it happen.