Wherever you go it is 'who you know and what you show'. To travel, on a low budget or backpacking to enormous cities such as Sao Paulo or Rio without having any contacts or friends there nor knowing the language, is difficult, low budget travel is much of a do it yourself affair, unlike business or high end travel, where the client is usually picked up at the Airport and driven to his, her or their hotel or resort in safety, what you show, anywhere in the world, money talks and trumps all. A low budget traveller with a bad section of direction could easily board the wrong bus lie or get off at the wrong Metro stop and wind up in a 'favala' (slum/marginal neighborhood) and be a target for a robbery, especially if wearing a backpack and consulting a guidebook on the street. (If you ever become lost in any large city, always get off of the street and go into a restaurant or store ask for the manager or owner for directions to your destination, in some cases and always late in the evening, it may be wise to call an authorized taxi. Many inexperienced travellers make errors in judgement on their first journey, take it all as a learning experience, don't generalize and put down an entire city, country or region because you failed to plan your your trip well in advance and did not use common sense after your arrival. Last week a woman visited us in El Salvador, a friend of mine took time out to show her around a bit in his a uto, she spoke poor Spanish, wound up insulting him by telling him he 'spoke bad English'....what you show...there are literally hundreds of off the beaten path destinations in Brasil and the rest of Latin America offering wonderful budget cultural, ethnic and eco tours escorted by native guides, often in remote areas, some of these interesting tours run as little as $15-20 per day per person with transport and often security, as in large cities, if not experienced don't wander around alone in remote areas. Many of these small and medium native operators, at least in the area of Latin america where I reside have even stopped 'targeting' backpacker/low budget travellers as most prefer to be 'independent' and save the money...thats ok.. your budget...but don't complain if the ---- hits the fan or the local buses to and from the site were 6 hours round trip, while the van took an hour there and back. etc. Most young locals are busy making a living and few have time to escort you around free. single women travelling in Latin America take care if strangers offer you rides and transport in their vehicle. Only accompany men you have been properly introduced to and never alone to remote areas or beach houses..at your own risk.
As for crime, about 70% of of the population of many Latin American countries is now under age of 25, in the USA crime is increasing as the adolecesent polulation increases, I was a young, angry and a bit wild male teenager once. In the favalas/barrios/slums/marginal areas of Brasil and Latin America are millions of poor people, who are not theives, however theives hide in these areas and often extort locals there, in many areas police and security forces are corrupt themselves and remember, now exist millions of cell phones in L.A., travellers coming from another country usually don't have a local cell, the theives do. Cuidase. Take Care.
Join one of the 'hospitality club' sites online, local bi and multilingual lingual members who will either host you or show you around their area, obtain country specific guide books and study up on your destination, along with detailed maps, surf the internet re: your destinations and start learning as much of the local language as possible via Internet, f2f tutor at home or language school after you arrive l.a. if you have the time.