I have 3 folders: Bike Friday New World Tourist, Dahon Boardwalk type and Brompton. I have been taking along all 3 in connection with work as means of local transport. All are steel. Of the 3, only Dahon would fit, and in fact quite well, into your budget. However, it is extremely klutzy in handling. I take it only on trains to destinations that are easy. Bike Friday takes a lot of time to disassemble and assemble. Only Brompton is of the type where folding or unfolding is completely uneventful and air transport too. The weakness of Brompton are limited gears. However the costs, including bags for transporting the bike and for carrying loads on the bike, take costs above 2k$. Pakit, that linberl has, might be a similar option but for a similar cost.