I've found that local metal suppliers and the scrap yard are the only options. When you factor in shipping, online places usually cost more. Occasionally, I get stock from Amazon, but only when it is on sale. Check the Hot Deals section for those.
Case in point, I just bought a 16' stick of 2x2x1/8" square steel tubing and a 12' stick of 2.5x2.5x3/16" square tubing for $92 yesterday. A full sheet (4x8) of 1/8 plate would have cost me $96 (I passed on that), but got a 30x30" piece of used 3/8" plate in the scrap yard for $24. Used steel runs $0.25/lb, new steel is close to $0.90/lb.
Up in AK, you are going to be limited, and online might actually work for you (if you can get flat-rate shipping or use Amazon Prime.