for example, try www.sanbornsinsurance.com or search for Oscar Padilla or Bajamex Insurance. Sanborns handle Mexico and Central America and maybe they can help you for South America too.You can arrange their insurance online or visit one of their agents e.g. in Tucson
How much time? it's up to you--- how much time have you got ?You could make a rapid transit in a few weeks or you could take months and months as you wander where the mood might dictate.How good are you at setting a schedule and sticking to it ?- difficult if you discover all sorts of side trips you can't resist, time flies by.
All insurance comes at a cost, the blanket CA coverage was about $148US for two weeks in '05, kind of expensive compared to what BZ, CR and NIC charge at their borders for their compulsory liability insurance, so figure out when/if you will be in those countries so you won't double up insurance for the time there.Too bad not every country offers it for sale right at the border posts
I can't remember the exact liability limits, but that is prettywell fixed, you either buy the insurance for the max or do without. Only liability is offered for motorcycles anyway.

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http://advrider.com/index.php?thread....207964/page-5 then scroll down to post #93