The bass shakers are truely awesome. I found an Aura bass shaker set with mini amps on ebay for less than 100$. Popped them under my pc chair... and fired mame up...
The results: At low volumes... the bass shake felt as powerfull as a 500 watt subwoofer at high volume! Setting the maximum power to the shakers resulted in me hardly able to view the monitor - because I was bouncing arround and made the screen appear to be shaking all over the place!
What makes it nice - is that you do not need the high volume to feel the power. .. whereas a subwoofer needs to move a lot of air to blast the bass vibrations. In many situations, theres actually more vibration from the shakers... because with a sub with low volume of air movement, you lose the impact. Bass shakers vibrate all the time... and you can feel every bit of it.
Obviouslty, a real powerfull motor to move the seat is completly a different experience. Out Runs shaker motor for instance, completely rocks. Maybe you could use the same type if setup as outrun.
Using a powerfull one direction motor, (and hacking a rumble pad) you could use a metal link arm... that moves the seat on a set of rails left to right rapidly. (simular to the old style trains)
However... remember that mame currently does not support Force Feedback yet : (
I highly doubt that 10$ jobbie would be sufficent or comparable to the power of a real bass shaker.