Thanks, everyone, for your comments and advice.

It seems that Oscar Calderon at Mexico Motorcycle Adventures in Mexico City (Inicio) can arrange for people to rent bikes and take across the border with a notarisation letter. He's incredibly helpful and gave me a very reasonable quote for a 400cc bike with all the necessary paperwork plus he will arrange having it returned back to Mexico. It makes a good back-up plan, but it's unfortunately still a bit expensive for me, so I'm still looking at buying a used bike.

Then I'm hoping to sell it in Panama (although a number of people have warned me this is a headache). Apparently I have to make sure to declare at the border that I plan to sell it and then pay customs fees and taxes etc. But at least it would still be some money back, whereas renting wouldn't.

At the moment I'm looking mainly in Mexico as there seems to be a wider selection of bikes available. My travel companion is very sure I should be going for not less than a 250cc, and probably not as big as a 650. So if anyone hears of one, please do let me know.

I'm also looking in Belize, and Emma at Alternate Adventures (Alternate Adventures | Motorbike Rentals and Alternate Adventures, Hopkins, Belize) says she sells off her 200cc dirt bikes regularly. So that's an option, although a dirt bike for such a long journey may not be very comfortable, right?

I'll also keep a look out in Guatemala - thanks for all the info, richsuz - and if you hear of a 250-400cc bike that's, say, around USD2,000, then please let me know. Is that price being too optimistic?

Unfortunately buying a bike in the US isn't an option at this point due to timing.

Richsuz: We'll probably reach Guatemala round August 15, and I will stay in contact to see if we can all ride together. It seems we're just whizzing through the eastern parts though for three days or so. But the itinerary isn't set in stone.


Cheers