Seriously? Watch any of the threads started by people that have done exactly what you're suggesting. I just glanced at one large F/X company. There online rate is about 10% worse then the current exchange rate for USD/EUR. The walk up rate at the company's shop would actually be worse.
Yes, seriously. Please read my post: I said small offices. These are the lifeline for expat workers, especially those that send home remittances. These businesses make their money in turnover volume rather than from single transactions. Even here in Geneva, one of the most expensive cities in Europe, the small, family-run businesses clustered around the central railway station provide excellent rates. Likewise, from my own experience, do similar businesses in Budapest.
No one gets the online rate shown on xe.com, a fact acknowledged by the website itself.