Hmmm, i've been looking for a 250 ish enduro type myself in US, but so far, not anything really attractive. Was hoping to find something like this :
http://www.sukidacycle.com/Enhtml/product_122.html

Good luck on your trip. I'd be VERY careful on choosing your route, especially the entrance to Mexico as parts of the border are dangerous as hell at the moment.

Seer