If you're lucky enough to own a recent Powerbook, and can program a little, you can write a g-meter program yourself and save yourself $200. The safety feature to prevent hard disc damage when you drop the computer is easily hijacked, so you could just poll it once a second and write it to a file. Have a look here for some cool examples:
http://www.kernelthread.com/software/ams/ams.html
Make sure you strap it down well before pulling serious gs!
Apologies if you're not as hopelessly geeky as me :-)