My house is 45 years old, plaster walls and a steel beam under the middle making it ridgid. Not like a slab but still very ridgid. Contimplated a platinum clark tranducer under the room ruled that out for a myriad of reasons including cost, wire complexity and effects of up to 1900 lbs of pressure to vibrate the room.
Decided on 6 Aura Bass shakers (4 for the couch, 2 for love seat) powered by a 300 watt BASH digital plate amp fed from the LFE from the Veledyne SMS-1 I figured was going to be plenty. 50 watts per shaker is right at its rating.

BASH is the supplier for the Outlaw LFM's. Its sold as a plate to be mounted in an enclosure. The back is not enclosed as some other brands. I fabricated a box for it. You could use an old reciever to push them. I like a dedicated sub amp because it has a phase control and standby mode as most sub amps do. At $150 its reasonable.

The net effect is "enhancement". I keep it the volume pretty low as it in my opinion it just be enough to fool the senses that the low end is really much higher. I think I can play over all system volume at lower levels and still have a very effective low end experience. Easier on the ears.

Breakdown costs are:

6 Shakers= $240
1 300 watt Bash amp:$150
Cables:$35
Lumber and hardware: $24

I got a $10 splitter from Blue jeans. I had some extra sub cables from another project. Not sure if "quality" really matters when your shaking the couch but The splitter also feeds the LFM-EX so its important.

Aura Base Shakers are a good product but there are other brands and configurations. A Google search will yield many discussions about this. Transducers are also very popular.

Its tough to qualify what result each product would have as each couch or chair design and installation is different. I set my budget not based on what I can afford but what I wanted to put in it. Originally I was going to use an extra reciever to power it to keep costs down.

Based on my couch design I had limitations. My couches have very little clearence on the bottom and are box spring construction like a bed would have. On many pictures of others projects on the internet I did not see anything that resembled what I had.

Net result is a bit over the top but thats whats fun about home theatre. I have a M&K 850 sub and the outlaw LFM-ex in the room. The M&K sits upfront with its LCR cousins and the LFM-EX in the rear. The Sub EQ keeps it all nice and tight. The M&K is more musical than the LFM-ex so the combo works out nice. If playing music only I shut off the Outlaw LFM.

I can't think of a new sub for under $500 thats going to move enough air to create the vibrations simulating "the end of the world or what it feels like when the Death Star nears its target!"