We were in SF in February this year and ventured into a photo shop down the hill from Union Sq. We had bought a 1Gb IBM Microdrive on the web (£180) before leaving the UK and were curious as to the cost in the USA (IBM being a US company etc.!).
They quoted us $480!! But the price plummeted when I said I bought one for £180.
My advice is to never pay the starting price, research prices first or go to an internet cafe to check before going back to the shop to buy. If they won't move on price, see if they'll throw in an additional battery or filter or card or just something!
Haggle haggle haggle
Good luck