If all you want is a cart with a griddle then it might be possible.  Most of the cost will be labor for the TIG welder and then the griddle.  The 24″ griddle width is no problem, the depth on most griddles is 30″ +/- due to exhaust and plumbing.

On a 40″w X 48″l chassis you can fit a 24″w griddle and one full size steam pan well.  That leaves about a 40″w X 18″l space.