Yup, readline's yank-last-arg command Alt-. or Alt-_ (see https://www.gnu.org/software/bash/manual/html_node/Commands-...) is the best off-the-shelf solution that still gives the ability to interactively edit the filename. To minimize the total number of key strokes I would suggest:

  mv foo.txt 
  ↑
  Alt-.

That is: intentionally run mv with only one argument (the command fails but is recorded in the history), Up arrow to recall the last command, and Alt-dot (pastes the last argument).

This is literally replacing an entire shell script with two key strokes (Up, Alt-.)