Affordable furniture in the Upper Midwest?

Hey all, I'm moving into a house in June and I've been slowly and steadily acquiring furniture for it. Does anyone know of good places to get secondhand antique/vintage bedroom furniture? I need all sorts of bedroom stuff--headboard, bed frame & mattress/box spring, dresser, etc. I'm hoping to spend less than $100 per piece, as most places I have gotten furniture so far have only charges $40-65 a piece for larger items.

I've kinda gotten all the good stuff from my usual haunts. If you're in southern Minnesota, northern Iowa, or eastern South Dakota, could you make any suggestions on where to look?
I've been shopping in Sibley, IA, Worthington, MN, and Sioux Falls, SD.

Thanks in advance!