This user script adds a button to your Steam badge pages allowing you to buy all the cards you need to finish a badge from the Steam Market at once.
My version is a single click do all. This means that clicking purchase will buy the cards, reload the page, and craft the badge. I take no responsibility for its use!
All credit to Doctor_McKay for creating the script and making the source available.
https://bitbucket.org/Doctor_McKay/steam-trading-card-bulk-buyer