If you want to buy a bike skip Brazil all together and go straight to Chile. Bike prices are quite high (an pre owned Honda CG125 can cost you around 3000 or 4000 dollars easily, 400cc bikes are around 8000 to 10000 dollars), taxes are outrageous expensive (I paid around US$ 200 to register my bike, an 125cc Suzuki, this year) and you won't be able to leave Brazil without having the bike with your name on the registration papers, and for this you gonna need to have a CPF (kinda of "Tax Payer registration number") that tourists are not allowed to get (kinda the Social Security Card in the US). The best options in your case, IMHO, are:
1 - Buy someone else bike with plates from another non-mercosul member country. Chile is the best option in South America but I have seen a lot of people riding on Peruvian plates. European or American plates are fine too, but I already heard people commenting that biker with american plates can be discriminated if some places here in South American, but I personally never seen anything like that. Argentine and Uruguayan bikes need the "Carta Verde" insurance proof to ride legally in Brazil and, in theory Paraguayan bike also need the Carta Verde insurance but I never seen a Paraguayan bike riding trough Brazil. Chilean, American or European bikes don't need to this insurance to legally ride in Brazil.
2 - Buy a Chilean bike. Tobi
can probably help you since he just traveled South America on a Chilean 125cc bike.
Suzuki GN125 2005
- Uberlândia / MG - Brazil
You don't need to have a big bike to have a great adventure.