I've cycled solo many times in Mexico. I've never encountered a problem with the locals. I've been down the Pacific coast in Guerrero and Oaxaca on Hwy 200. I've also cycled the Yucatan and Chiapas. Never a problem.
You can check out my itineraries, costs, distances, photos at
www.geocities.com/pathebikeguy/oaxaca
www.geocities.com/pathebikeguy/guerrero