I built these for $50 apiece. Go down to the local big box hardware store and buy a hollow core door. Get the one WITHOUT the hole aready drilled for the door knob. They cost $20--$30 depending on how wide you want. I have a 24" door and 2 of the 32" doors.

Wrap the perimiter with 2x4s and add legs. It's not a bad idea to add a shelf about 24" off the floor. It's handy and helps keep the frame rigid.

Buy some screw-type adjustable feet for it and level it up.

I use 3" drywall screws for the frame. I only put 4 screws on each side and 2 screws on each end. Then slap a piece of 3/4" plywood on the shelf. I used 1.5" drywall screws for that.

When the door gets used up and full of holes and saw marks--just pull the screws from the perimiter and flip the door over. Brandy new building surface.

I haven't got the shelves in yet when these pics were taken, but you get the idea.

How high should my bench be?
Easy:
Stand up and drop your arms down to your sides. Now bend your elbows at a 90* angle and point your hands straight out. Thats the height that you want the table. Maybe a few inches lower--not to exceed 6" lower.

Mine are 42" off the floor.