I have all of the parts and pieces to build the cart you want, including the griddle. If you are good with hand tools, can cut wood, paint, glue and screw, you can build your own for around say $1300. I think that is about what I have invested in all of the parts including the griddle. For an extra $500 more or less, you can also have a 12 volt top load refrigerator/freezer unit.
If you have the space and time, you could easily build this yourself and have one hell of a unit with money left over to buy all of the other needed stuff to get started.