Actually a bin will cost substantially less today then it would have a year ago.  We spent about a dollar per bushel last year before the runup in steel.  You basically can't build a small bin economically in today's world.  

If you are looking to ship it more-less immediately, why not just pile it and skip the bags?  They pile down here in the fall and start to move out in about a month, and I'm sure we have far more rain during harvest then you do.