One way to remove mods is to 'reforge' your weapon. I did that with my hunter's rifle, and it got rid of 1 of the 2 mods on it. Not sure if it still does that, or does it with anything else...
pretty fun. Wasnt too hard to beat though. After about the 30k mark of trading, i stopped. I earned the rest just by travelling around. Finished with about 90k or so...