You can pick up two Aura Pro transducers for around $100. For even cheaper you can pick up two Dayton BST-1’s. I’ve never used the Dayton’s, but I have two Aura Pros (one bolted under each butt cheek).
I bought my Aura Pro’s in a bundle with a 2 channel 150watt Dayton amp, Dayton Audio APA150 Amp With 2 Aura Pro Bass Shakers Bundle
Here is the same bundle with BST-1’s, Dayton Audio APA150 Amp With 2 BST-1 Bass Shakers Bundle
Aura Pro, Aurasound AST-2B-4 Pro Bass Shaker Tactile Transducer
BST-1, Dayton Audio BST-1 High Power Pro Tactile Bass Shaker 50 Watts
This will give you an idea of what is available on the market, Exciters & Tactile Transducers
I plan on adding two more, smaller, transducers under my rudder pedals. The ones on my seat shake my seat, stick, and throttle.