Definitely stick with the cross bikes. The flat bar road bikes you mentioned may not have enough clearance to put a knobby tire on so you won't be able to ride off road at all with them.
Have you thought about the Surly bikes? The Cross Check is a nice steel frame for not much money. It's also available as a complete bike. You may want to look into building it up though to get it exactly as you want. It also has bosses on the rear triangle to mount a rack (not sure if that's important to you).
ETA: This link has a huge list with links off basically all the cross frames out there. Some of them have pricing, but some are listed for Frame only while others are for complete bike. Thought you might be interested:
http://www.bikeforums.net/showthread.php?t=258177



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