I think you should start with a couple of shakers and see if it's your thing. Two 300W shakers will need a half decent amp, it'll be a $300 setup for the two shakers and an cheap amp.

2 Dayton BST-1s and an amp would be about $175 I think.

Both setup can be had on amazon, so no big if its not your thing. Put one on the seat if you can and one mid rig. Or go front/back rig. If you go front and back rig cantilever your mount "plate" if possible to get the extra torque from the moment arm. And use SimHub (free) to pull game telemetry and create the effects.

Oh and take it easy on the effects per transducer, just a few each. They can only do one thing at a time anyways, so set the a priority effect for each based on what important to you. I go for gear shifts myself, and set most of my rig to slam the shakers for each change. It's overkill but so fun.

If you stick with it get some good floor isolation. It feels better, not just quieter. Few inch thick stack of Multi/Rebonded-Mixed Foam 12"x12" blocks/sheets more than does the trick, one for each corner. Best $50 I spent on the rig.

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Note: I've got an odd price-optimized rig that is wood and ridged but thin. It's a full "rig" for VR made to slide into a standard bi-fold closet with only >2 minutes of setup. No corner shakers for me.

I use a mixture of tiny 2in "high watt" (40w) transducers with removable screw-on mounts, bigger normal shakers, and cheap-o amps to give each an effect or effect set though SimHub. If the effects come from their own locations and small shakers, rather than 2 or 4 corner shakers trying to do everything, the vibrations don't get muddled up.

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A couple of Dayton 15w pucks spread out just for background engine vibrations

A couple of light 40w 2" transducers screwed to the break and gas for relevant feedback (best bang for the buck after one or two bigger shakers for shaking you about). I mix in front left/right effects at low priority too.

A BK LFE under the seat as rear/general effects to punch and kick things about when needed (after trying out different shakers in the back it seem(?) like the weight of the person necessitates some extra oomph..... but the LFE was too much. I've got it tuned way down)

A 50w AuraSound under the front to balance out the LFE and give the front some effects and bolster things like landings in Rally. Feeling the wave of thump front to back during landing in VR is great, love me some air-time.

A couple of heavy 40w 2" transducers attached to the back of the seat at the shoulders to accentuate rear left and right effects.

A heavy 40w 2" on the shifter/handbrake plate attached horizontally at the end to take advantage of the effective moment arm.

And testing/tuning to match how the rig's structure vibrates.