Yes, they own the script. Developers do this all the time by the way, it's part of the job to automate as much as possible. No developer will think about selli

Yes, they own the script. Developers do this all the time by the way, it's part of the job to automate as much as possible. No developer will think about selling a script for $800 to their current employer, that doesn't make sense. What you should do instead, is making sure you get credit for your script and not one of your colleague or your boss. And try and get a raise at some point.