Welcome to the touring life! It's fun ain't it?

Before going farther, search this forum for the keywords "mtb", "mountain bike" and "cyclo cross". Many folks use cyclocross bikes like the Surly Cross Check. Also check crazyguyonabike.com and look for people who have toured off road and what they used. Many examples there. 1200 is plenty, but you'll have to choose between used and new, converting a hardtail mtb machine or buying a stock commercial build. Depending on how rugged your off road touring is, even a normal touring bike like a Long Haul Trucker will do fine with the right tires. My 2 cents: stick to 26" tires for off road use but 700c/29er is fine if you intend to stay in the US. Remember to budget for racks, fenders, panniers, etc.