Who do you Gus usually talk to to negotiate? There is a vintage p in a California store and hey told me they don't negotiate or price match (understandably) on vintage stuff...didn't know if a call to a corporate office would help.
[Dr. Phil voice] What you need to do[/Dr. Phil voice], is find another one worth buying, hopefully at a better price. Then, walk into GC with cash in hand (vintage stuff (tagged vintage) isn't returnable under the satisfaction guarantee (as far as I know) so I wouldn't feel bad about paying cash), talk to the store manager and let them know that there is another similar bass that you're considering and work out a deal with them. If they won't budge, be prepared to walk away.
You might want to use the old car buying technique of giving them your contact info and tell them that when they're ready to work with you on price to give you a call. In the meantime just pursue the other bass.