I'm currently using a school desk that I got at a yard sale for $15. It most likely originally came from an auction where the fellow bought a "lot" of discontinued desks. It has a Formica top and a shelf all the way across underneath that would likely be the right depth for inserting your machine to get a totally flat work surface. I have an old cabinet model machine positioned beside the desk for extended work surface of approximately the same height. The desk is easy to move but does not fold up for true portability.
Gives you another avenue to explore if you think this might work for your purposes.