If you want the essential Portland destination then I would refer you to SCRAP.
SCRAP sells recycled bits of detritus that its received as donations. While that may sound like countless other non-profit retail outlets you can think of, the big difference is that SCRAP sells its stuff (for lack of a better word) at ridiculously low prices. It's goal is to put art fodder in the hands of the masses, and it succeeds admirably. The clientele is actually eclectic, not just hipster-eccentric (although they find their way there too). I've watched people in SCRAP find objects that they immediately love— maybe they love them for their potential to be something else, or maybe they just love them for their living room. SCRAP appeals to the thrifty, the creative, and the curious: all of which are part of the spiritual core of Portland. When I buy things at SCRAP I linger over them and revisit them and treat them like the bits of treasure that they are, and I can do that without ever suffering from acid reflux on their behalf.
Yesterday, SCRAP had an entire bin of 11" x 14" fiber and RC prints (in black and white as well as color) that a photographer had relinquished from his archives. Undoubtedly he'd gone digital. While many of the prints were product shots or early-90's big-hair studio lighting stock photography there were a few quieter gems: a muzzy black cat pawing across a linoleum wasteland, and a flock of birds creating a cloud of punctuation in the sky. Each cost a dollar.
In a small tub next to them there was a small stack of images labeled MEDICAL PHOTOGRAPHY. I picked out half a dozen and then happily plunked down my two quarters. It intrigues me that in a digital world some of the finest and cheapest images I've encountered in months are printed on paper using very expensive imaging equipment. Obviously, that is a bit of circumstantial irony, which carries a lot more bite in Portland than fabricated irony.