Sturdy Turntable Stand

uberwaltz,

"...which then sit on steel pucks on my tiled floor with felt cushioning them."

Is the whole floor tiled or just area under those steel pucks?

Check out Timbernation.  There are options way under $3k. They will also custom make anything you want.

Uberwaltz if you can jump up and down in front of the turntable and put the edge of a stethoscope against  the platform with music at a moderate volume and not hear an increase in the volume through the stethoscope you are good to go. No other mods needed. Next put the stethoscope against the base plate of the Garrard. You should hear no increase in volume. If you do you have a plinth issue. Turn the turntable off and play another source. Listen to the platter mat on and off. 
A sturdy stand on a concrete floor is always the best. Trying to predict which plinth and turntables are going to have trouble is difficult and frequently surprising. Some turntables depend entirely on their stand for isolation others you could could put on a folding table and they will do fine.  

*geofkait*
So, what do you use or recommend?

Geoffkait just don't live next to the highway or train. Where I live we have had one earthquake in 28 years it lasted 10 seconds. If you wan to spend money to protect your system from a 10 second event knock yourself out.
Actually, if you live in a sky scraper the wind can sway these buildings and move them several inches. This is what caused the windows to pop out of the John Hancock building in Boston. A few inches would definitely cause many turntables to launch their tonearms. So us vinyl guys would do well staying away from sky scaper apartments.