Regarding practicing with a weak tool:
In addition to the dojo, I also teach an intro to martial arts class at the college near here. We spend a few weeks doing aikiken. Because the school wasn't too crazy about dropping $50 a pop on 30 white oak jo, I had them buy red oak at $10 apiece. The first semester, I was trying to get the students to stop putting so much muscle into their cuts. So I had a student stand with her bokken held in one hand out in front of her, perpindicular to the direction of my cut, and performed a cut tensing all my muscles the way the students were. Made a noise, no big deal. For the second cut, I just relaxed and pretty much let the bokken I was using, also red oak, fall onto the student's. The tip of her bokken broke off and stuck three inches deep into the wall behind me.
Now when I do that demo, I always make sure I have my white oak bokken with me, with a spare for the student.
We get our bokken and jo from http://www.tozando.com.
We use the one they call the Aikido bokken, which has a design similar to the bujin bokken. However, the tozando bokken is heavier than the bujin bokken I've held. The two weapons run about $100, including 3 day air shipping. I've never seen one break. They are a little heavier than the $40 bokken from Kiyota company. I also have a bokken from Kiyota Co. (it's only a 45 minute drive away from me. A friend of mine used to work there. Kiyota-san is a funny guy) called a keishi ryu bokken. Much heavier, really good if you want to go banging. Can't remember how much it cost because I've had it close to ten years.