The cheapest (in terms of efforts) way to mount mic stand to a table with slanted edges
A piece of a board between the clamp and the tabletop should work.
If not sturdy, then drill a hole in the clamp arm and use a screw to secure the end of the board.
You could also attach the board to the underside of the table with doublesided tape.
If you cannot find wood, then get a cheap plastic cutting board meant for kitchen use.

Another possibility, but not cheapest is to drill a cable hole, and pass the clamp through the hole.