If you go to the store to get it, explain the situation to the cashier and ask her to give you the online price. If he/she cannot help, ask to speak to a manager. I'm fairly sure they'll make you happy (they definitely would in my store 6668). :-)
Call the store manager and ask to have it added to your order as BOPIS (Buy Online, Pickup In Store).
Call the local store manager and see if can be added to your order as a BOPIS (buy Online, Pickup In Store).