To explain a bit further, I've been asked to become an advisor for the engineering classes at a local high school. The staff was soliciting project ideas, and I suggested that pinball games can be an excellent mix of engineering disciplines. The teacher agreed and so now I'm helping look for machines. I suggested Zizzle and Sentinel machines because they tend to be less valuable, a little more simplistic and look easier for a small team of high school students to manage(not to mention the fact that I wouldn't wince at a kid gutting something like that). The students have a wide array of tools available(from CNC milling machines to 3D printers), so the idea is for them to build their own driver boards in conjunction with micro controllers and perhaps Raspberry Pi's for the more advanced kids. Eventually, we would like the kids to take a year designing a game from scratch.
For those interested, the students are working on projects like this right now:

(That finger was a precursor to a full arm, which is now complete, controlled by a glove with flex sensors)

Anyway, if you have a machine like that that you wouldn't mind letting go for cheap to help us out, it would be much appreciated. Thanks!

Just an update. I found one for $50. The power supply is torn up, and the pop bumpers didn't seem to work. The general idea now is to debug the bumpers, replace the buttons with real arcade buttons and then present the game to the kids along with some discussion of the way "real" pinball games work.
Some future projects:
1) Create new driver and control boards.
- The kids are currently using Arduinos with custom shields(that they designed and built) for robotic arm controllers. I expect that it will be trivial for them to utilize Arduinos for this project as well
2) Create a new theme
- The only problem here is getting the kids to agree on a single theme. It seems that everyone has their favorite, so this might require some intervention to make sure it doesn't get stuck on the initial design phase.
3) Building full sized custom games
- The end goal here is for some of the more talented and driven engineering and art kids to collaborate on some full size custom games. They would start with milling out a playfield, after perhaps testing shots in a VPin environment. We could also work halfway and give them some populated playfields to start as well.

If the Zizzle modding goes well, I may end up picking up more for the beginning students to hack on.