Hi, Im Roberto, Im Chilean
1st, you don't need a carnet for Chile or Argentina or any other country in America.
2nd, If you will buy the bike in Iquique, you will have some problems... because Iquique is like a DutyFree port or something like that, the prices are cheapper, but with the vehicles there are special laws. If you buy a vehicle in Iquique, it must stay there, in the region, because they don't let you have a "zona franca" vehicle outside the "zona franca". the only people that can do that are the people who lived in Iquique for at least 5 years. Other people can buy vehicles too but the have to return to Iquique every 3 or 4 month (I don't rember exactly) to check with the autorities that the vehicle is staying in the zone. Not even we who live in Santiago can buy vehicles in Iquique.
the prices of the bikes in Iquique are lower, like a 20% lower, but there not to many bikes to buy. here in Santiago you will find a better "catalog". for example, a DR650 1996 you can find it for like US$3000.
The registration procces is very fast. you need to go to a "registro civil" with the owner and make a "contract". you can do this directly on the registro civil (some minutes slower, but cheaper, and you get the first papers to your name inmediatly) or you can do it on a "Notaria" (more expensive, and you will get your papers later). IF you do this paperwork on a big Registro civil office, some times they give you all the papers done at the same moment, if is a small office, they send it to your place of stay, and takes like 2 weeks.
the final paper, that says that you are the owner is the "padrón"
to do all this paperwork fast and with no problems, the bike must to have some papers on rule:
-obligatory insurance
-permit of circulation
-technic revision
all this has to be on rule, not necesarly on your name, only the "padrón" is in your name
all the process, will cost like 50-100 bucks if the bikes is relatively cheap
just come down here and I can help you, is relativelly easy and fast! I will glad to help you, Im a adventure biker too
cheers!!!
pd. sorry for my stinky english!!!