For the past almost five years, Chicago-based real estate investment firm Zeller Realty Group has been itching to get into Portland. Now, they're in. ZRG has purchased the Umpqua Bank Plaza at 1 S.W. Columbia St. in downtown Portland from Shorenstein Properties. Several local sources confirmed the price was $90 million. Shorenstein paid $84 million for the 19-story building in 2007. "We love the demographics and the fundamentals of the Portland market," said Bill Rogalla, director of acquisitions…