Define cheap?
Fast
/ \
Cheap -- Good
Pick two.
I'd start with a 4x8 piece of 3/4" CD ply, frame one side of it with 2 or better 1x4 with stringers every two feet. Install a set < 2> of straight < non swivel> casters on one end of the framed side, and a set of swivel in the middle and opposite ends of the
platform. Now flip it over.
Build two 4x8 Broadway flats, but
cover them with 1/8"< cheap> or 1/4" <good>
luan, which is usually available at Home despot or Lowe's or wherever, 'though you'll probably need to ask for it as "Door Skins"
Make sure to set you toggles at heights compatible to cutting a "window" into each
flat. Paint the flats and the
platform their
base colors. Attach, by screwing through the bottom
rail into the framing of the
platform, the flats to the upstage side of the
platform. Go to Harbor Freight, buy a couple of cheap "wrought Aluminum" garden benches. Assemble benches < good luck> place one bench in the "middle" of each
flat, perpendicular to the wall. Figure out a good place to screw through the back of the flats, preferably through a
toggle, into the ends of the seat slats of the garden bench. Screw the feet of the bench to the top of the
platform, Have your kids sit in the bench.
Mark an appropriate to place to cut a window into the middle of each
flat. Cut out the window and frame it with 1x2 adding Mullions, if you want.
That's a quick and dirty way. 'Course you could also add a shelf over the top of the benches, with Wrought
Iron looking shelf Brackets. You'd need to add a piece of tubing <
conduit> at each end of the shelf to run to the top of the
platform to help stabilize the center of gravity.
Adding the straight
caster to one end makes the entire
unit much easier to steer, so it doesn't vector or slew off at an angle. If the
unit is going to be stored in the wings and brought straight off and on then use all straight casters.