First take a look at this video of the Tennis Twist, the cheapest ball machine on the market.
I'm thinking: yeah, 15mph is ridiculous. But would this machine still help me improve my volleys? I'm a 3.5 borderline 4.0, and I'm really having a hard time with my BH volleys, they're not crisp, and I think it has something to do with my contact point (among other things). Anyways, I thought if I'd position myself closer to the machine and tilt it so that it would throw a decent ball to my backhand, it could help my volleys.
Another benefit: I could use it in my basement (I live in Canada and renting an indoor court during winter is expensive).
What do you think?