The fact that the store is a big chain actually serves to decrease your chances of successfully negotiating a better price, imo. There is very little local pricing autonomy (ability to think and act for oneself) afforded to local managers of chain stores. I doubt you will have any luck at all if it is an REI or something.
That being said, $50 off a $400 bike is not unheard of and if the entire chain is local, that might be entirely different.
Good luck.