I use an old Steelcase Dot matrix printer stand I got at an office furniture surplus/recycling center. It is as solid as a rock, has adjustable height and leveling and was only $15.
The top is nearly 2" thick and has about 8" of height adjustment. The stand also has a shelf that was made to hold perforated paper that feeds up through a slot in the center of the table. My Beseler 45MXC fits perfectly.
On a concrete floor, the only vibration comes from the enlarger itself.