Send your explorer to the Aztecs and buy all their cities in exchange for an alliance and some 18000 per turn (3 turns). If you haggle it is possible to get it cheaper. The Aztecs are almost gone and after four turns your economy starts to work if you make Vera Cruz you capital. Finish the Aztecs and prepare for the Mayans. All cities can produce conquistadores in a few turns so that won´t be difficult.