You can get the plate jacket for 400 if you buy it when you're clearing the "boulder" from the train tracks. You can also score some extra cash by using the talk option on that shop keeper; she'll have you clean out her silo of monsters for 500 gp, not to mention you get the money from killing the stuff inside.
Having a badge is kinda pointless if the walkthrough is right there...basically you're handing out 30 points for taking the time to read the walkthrough and do it.
if you can't get the badge, I have two words. Antimatter shield. So easy to win with that, even though the level 50 boss still takes like ten minutes to kill with maximum damage bonus.