The foundation of the table was in the legs. I created the legs out of 2 x 4 studs that were roughly $3 for an 8 ft. piece.
After attaching the legs to the table tops, I needed to add some supports to the legs to keep them from folding in on themselves. These supports were made out of furring strips from Lowes. You can get them in bundles of six for about $1 a piece. They are 8 ft long and 1" x 2". They aren't the highest quality and have some knots, but work fine for this project. I placed beads of glue on each piece that would make contact with the top and/or legs. I also used finishing nails to add additional strength.
There was a horizontal support that went between both legs on the ends of the tables. This horizontal support was attached using glue and finishing nails.
I wanted each table to be moveable so I added lockable casters to each wheel. They were 2" Lockable Casters for $2.47/each from (Menards) (I had to order these online). They are threaded so I added T-Nuts to each leg that allowed the caster to be screwed in. However, I had to add two screws with washers to the edges of the T-Nuts to keep them from falling off. In hindsight, I would have bought casters that you attach with screws instead of a threaded shaft.
I used a table saw to notch out all of the furring strips. I set the fence 1/4" away from the blade. I then ran the furring strip through the table saw to create my first notch. I then adjusted the fence so that it was 5/16" away from the blade. I repeated the process of running the furring strips through the saw. I did two different distances so that the notch had some play when the whiteboard panel was slid into it. Only one pass at 1/4" created a very tight fit for the whiteboard panel and didn't allow it to slide at all.