The Real Azteca Hotel is one block from the shoe shopping plazas and seems quite nice, reasonably clean, air, wifi, restaurant for only $600 pesos taxes in August 1, 2007.
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Midrange
Hotel Mexico Plaza*: Free Wi-Fi, though somewhat distant from the main city around 20-25 minutes on a cab. Taxis from the airport are by no way cheap, around 20 USD, and transportation to downtown is around $5USD. Rooms start at $80USD the night.