I would try Priceline (of course....). Right now, it looks like the Radisson and Holiday Inn downtown are sold out for that weekend. The Duluth Sheraton is going for $149 right now. In the past it has gone for $50/night when listed at $149 per their website. It has also gone up to $75 (listed at $249). Start at 3* $50 and work your way up. The Sheraton is a bit further from the DECC, but it's new, and also on the skywalk system...and definitly walkable. I'd stay away from Inferior unless desperate.