I'm currently designing a racing wheel chassis that contains a racing
seat, force feedback wheel, and gas/brake pedals. I plan on adding a
device that uses the audio feed from a PC or console system to move a
motor that attaches to the seat or other part of the unit and vibrate
it.

The base of the unit is a 2' x 6' x 1" board, supported by 4" x 4" x 4"
blocks connected by 2x4's. There are 6 4x4 blocks and 7 2x4's
connecting them. Looks like a digital figure 8. For the motor to be
able to effectively shake the chassis, the chassis will need some form
of suspension. I'm thinking that attaching it to the 4x4x4 blocks would
be best.

The total weight of the unit and human shouldn't exceed 300 lbs. I'm a
suspension novice and would like to know if something in the automotive
field could accomplish this cheaply (under $100). If not, what else
could be used?

Any information is appreciated, thanks in advance.