Well, I made my first batch of soymilk from my brand-spankin' new Soyabella machine. It's a relative breeze to do. The only time consuming thing is soaking the beans for 6 hours. Since I can get organic soybeans for about $1.50 a pound and you only use a little cup worth, my soymilk is going to be pennies per gallon. You can also make raw nut milks (like almond) in it too.
Anyway, another fun thing you can do with your homemade soymilk (I suppose you can do the same thing with store bought plain soymilk) is make your own tofu. I'm guessing that this will result in another super-inexpensive homemade item.
Once you've cranked out your soymilk, all you need to do is add a coagulant (like nigari), let it sit for 20 minutes and then put it in a press. Et voilà! Tofu. Again, for pennies on the dollar.
Now, I just need some good tofu recipes...