Four level to go one this based on price/performance. With each incremental upgrade the difference is clearly perceptable. But this also depends on the resolution of the rest of your system and your room.
Also, try a bag of lead shot on top of the player. Or a VPI magic brick.
1. Vibrapods or Herbie' Audio Tenderfoots ($6/per, $8/per better)
2. Final Laboratory Daruma ($99)
3. Stillpoints ($300)
4. Any of the above with the addition of a Black Diamond Racing shelf under them. ($500)
5. Or go nuts with a Grand Prix rack ($2500)