What is under your TT, cheap islolation?

I would first make certain that the legs of your rack are sitting on top of your floor joists opposed to on the plywood between the joists. This will give you the most stability. You don't want to use anything that isn't rigid under the table. I use granite but it's not really inexpensive. You might want to try a large paver block 18" x 18" or something in that nature.

The bouncing is the result of vertical displacement from the movement of the floor. This will occur without regard to the type of isolation you use so long as the TT is supported on your floor unless your floor is braced to avoid flexing. Suspended TT's are especially vunerable to this type of movement, thats why folks recommend wall mounting. Interestingly unsuspended tables can often work reasonable well over such a floor. You could try using a large rigid platform under your stand insuring that the edges of the platform overlaped the floor joists. That might help but it might look quite ugly depending of the width of the joists and composition of the platform.

Most isolation devises are designed to deal with small vibrations. The vertical displacement is not really a 'vibration' that they are designed to deal with. If you can not eliminate the vertical displacement then the only thing that makes sense to me is to use something soft under the table like an air bladder based support.

FWIW

Not sure how cheap is what you consider as cheap but ...

As a turntable platform, I use two 24"x25"x1.5" maple counter tops laid flat on top of each other, separated by a cork sheet (1/16" I think), placed on Mapleshade brass cones.

It looks nice and really does wonders for isolation.

Regards
Paul

Look into suspending the turntable from the ceiling. That solves footfall problems and is effectively better than the 'self on the wall solution'.
Bob P.