I reside in Idaho and am about to purchase my first home. I submitted a purchase offer on a home that was countered, then I accepted the counter offer. The Seller Disclosure statement clearly said the home was not in a Flood Plain, but I clearly found on the FEMA site that it is in fact located in a 100 flood plain, and my mortgage application now requires a hefty fee for a Certification and Flood Insurance. What are my rights to 1) Back out of the deal; and 2) to proceed but somehow hold the seller financially accountable for the additional costs.

You can certainly back out of the deal, and you should be able to get your deposit back without penalty. But if you still want the property you can go back to the seller and try to negotiate a price cut to you. You may find that in this market he's wlling to lower the sale price. You shouldn't wait until after the closing to do this - the fact that you know of the problem before closing pretty much shuts you out of any redress afterwards. However, check with your lawyer in Idaho to see what he would recommend.