When you say you're allowed to bring in two vehicles - I presume it's one per person - are you meaning two vehicles duty free
? That's my guess and if correct wouldn't it be cheaper to bring a 3rd one in and just pay the import duty rather than buy one there?
I've only ridden to MX a couple of times [last year] and I had to post a deposit based on my bike's value which if I didn't "export" it back to the US within the time period on my temporary "import" permit I'd forfeit the deposit. I'm told the idea behind this is to curtail the practice of taking vehicles into their country and selling them thus avoiding import duties. All of that makes sense and it was easy enough to deal with but my reason for mentioning this is the deposit on my 2006 Ninja 650R was only around $325, not much in my thinking and if that reflects how values are assigned it would follow the duty on a small scooter wouldn't be a lot. See where I'm going with this? From what others say about the high cost for bikes purchased in Mexico maybe paying the import fee for one you bought cheaper in the US would be the ticket?
Anyway best of luck with your move to the sunnier part of the world!